{{Redirect|CIS}}{{Redirect|CIS}}{{Redirect|CIS}}{{Redirect|CIS}}{{Redirect|CIS}}{{Redirect|CIS}}
Metrication in the United States is the process of introducing the
International SystemSi, si, or SI may refer to :- Places :* Mount Si, a mountain in state of Washington* Si County, county in Anhui, China* Si River, a river in China* Slovenia, a European nation Si, si, or SI may refer to (all SI unless otherwise stated):- Places :* Mount Si, a mountain in state of Washington* Si...
of units (SI / Système International) to replace the customary units of measurement that are the primary units of measurement in the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
. This
processMetrication refers to the introduction and use of the SI metric system, the international standard for physical measurements. This has involved a long process of independent and systematic conversions of countries from various local systems of weights and measures. Metrication began in France in...
has been largely completed in most other nations of the world but in the USA has been unsteady with no definite conclusion. The U.S. uses a mixture of units of measurement. In some fields, the
metric systemThe metric system is an international decimalised system of measurement, first adopted by France in 1791, that is the common system of measuring units used by most of the world. It exists in several variations, with different choices of fundamental units, though the choice of base units does not...
has been used in the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
since the early 1800s. The use of metric units instead of or in addition to
United States customary unitsThe United States customary system, or American system and sometimes "English units", of units of measurement is the most commonly used system of measurement in the United States. It is similar but not identical to the British Imperial units. The U.S...
has been gradually increasing for many years, but much of the public momentum has been lost since the 1980s, except in
schoolA school , is an institution designed to allow and encourage students to learn, under the supervision of teachers. Most countries have systems of formal education, which is commonly compulsory. In these systems, students progress through a series of schools...
s,
scienceScience is in its broadest sense to any systematic knowledge-base or prescriptive practice that is capable of resulting in a prediction or predictable type of outcome...
, and
manufacturingManufacturing is the use of machines, tools and labor to make things for use or sale. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale...
. While other countries use the metric system predominantly, the USA has continued largely with customary units. There has been little political will to continue conversion.
19th century
In the early 1800s, the U.S. Coast and Geodetic Survey (the government's surveying and map-making agency) used
meterThe metre or meter is the basic unit of length in the International System of Units . Historically, the metre was defined by the French Academy of Sciences as the length between two marks on a platinum-iridium bar, which was designed to represent one ten-millionth of the distance from the Equator...
and
kilogramThe kilogram is the base unit of mass in the International System of Units .[The spelling kilogram is the modern spelling used by the International Bureau of Weights and Measures , the U.S...]
standards brought from
FranceFrance , officially the French Republic , is a country located in Western Europe, with several overseas islands and territories located on other continents. Metropolitan France extends from the Mediterranean Sea to the English Channel and the North Sea, and from the Rhine to the Atlantic Ocean...
. In 1866,
CongressThe United States Congress is the bicameral legislature of the federal government of the United States of America, consisting of two houses, the Senate and the House of Representatives. Both senators and representatives are chosen through direct election....
authorized the use of the metric system and supplied each state with a set of standard metric weights and measures.
In 1875, the United States solidified its commitment to the development of the internationally recognized metric system by becoming one of the original seventeen signatory nations to the Metre Convention or the Treaty of the Meter. The signing of this international agreement concluded five years of meetings in which the metric system was reformulated, refining the accuracy of its standards. The Treaty of the Meter established the
Bureau international des poids et mesures (BIPM, International Bureau of Weights and Measures) in Sèvres, France, to provide standards of measurement for worldwide use.
Under the
Mendenhall OrderThe Mendenhall Order marked a decision to change the fundamental standards of length and mass of the United States from the customary standards based on those of England to metric standards. It was issued on April 5, 1893 by Thomas Corwin Mendenhall, superintendent of the U.S...
in 1893, metric standards, developed through international cooperation under the auspices of BIPM, were adopted as the fundamental standards for length and mass in the United States. The U.S. customary units such as the foot and pound have been defined in relation to metric units ever since.
The 1895 Constitution of Utah, in Article X, Section 11, originally mandated that: "The Metric System shall be taught in the public schools of the State." This section was, however, later repealed.
20th century
The Conférence Générale des Poids et Mesures (General Conference on Weights and Measures) is the governing body for the metric system and comprises the signing nations of the Treaty of the Meter. The Conférence Génerale des Poids et Mesures approved an updated version of the metric system in 1960 named
Le Système International d'Unités (
International System of Units) and abbreviated
SISi, si, or SI may refer to :- Places :* Mount Si, a mountain in state of Washington* Si County, county in Anhui, China* Si River, a river in China* Slovenia, a European nation Si, si, or SI may refer to (all SI unless otherwise stated):- Places :* Mount Si, a mountain in state of Washington* Si...
.
On February 10, 1964, the National Bureau of Standards (former name of
National Institute of Standards and TechnologyThe National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory which is a non-regulatory agency of the United States Department of Commerce...
) issued a statement that it will use the metric system: {{cquote|Henceforth it shall be the policy of the National Bureau of Standards to use the units of the International System (SI), as adopted by the 11th General Conference of Weights and Measures (October 1960), except when the use of these units would obviously impair communication or reduce the usefulness of a report.}}
The metrication of the United Kingdom and the other
CommonwealthCommonwealth is a traditional English term for a political community founded for the common good or in which all participants have equal standing...
nations, particularly Canada, increased the need of metrication in the United States.
In 1968, Congress authorized the U.S. Metric Study, a three-year study of systems of measurement in the U.S., with emphasis on the feasibility of metrication. The Department of Commerce conducted the study. A 45-member advisory panel consulted and took testimony from hundreds of consumers, business organizations, labor groups, manufacturers, and state and local officials. The final report of the study concluded that the U.S. would eventually join the rest of the world in the use of the metric system of measurement. The study found that metric units were already implemented in many areas and that it use was increasing. The majority of study participants believed that conversion to the metric system was in the best interests of the U.S., particularly in view of the importance of foreign trade and the increasing influence of technology in the U.S.
The U.S. Metric Study recommended that the United States implement a carefully planned transition to the principal use of the metric system over a decade. Congress passed the
Metric Conversion Act of 1975The Metric Conversion Act is an Act of Congress that then–U.S. President Gerald Ford signed into law on December 23, 1975. It declared the Metric system "the preferred system of weights and measures for United States trade and commerce", but permitted the use of United States customary units in...
"to coordinate and plan the increasing use of the metric system in the United States". The Act did not stipulate the conversion happen over a decade. Voluntary conversion was initiated, and the U.S. Metric Board (USMB) was established for planning, coordination, and public education. The public education component led to public awareness of the metric system, but the public response included resistance, apathy, and sometimes ridicule (for example, the
Saturday Night LiveSaturday Night Live is a weekly late-night sketch comedy and variety show filmed in New York City. It made its debut on October 11, 1975, under a slightly different title. The show features a regular cast of comedy actors, joined by a guest host and musical act...
decabetThe Decabet was a Saturday Night Live sketch in which Mr. Joseph Franklin of the U.S. Council of Standards and Measures introduces the new "metric alphabet"-the "Decabet". It originally aired on April 24, 1976 ....
sketch). In 1981, the USMB reported to Congress that it lacked the clear Congressional mandate necessary to bring about national conversion. Because of this ineffectiveness and an effort of the
ReaganRonald Wilson Reagan was the 40th President of the United States and the 33rd Governor of California .Born in Tampico, Illinois, Reagan moved to Los Angeles, California in the 1930s...
administration to reduce federal spending, the USMB was disbanded in autumn of 1982.
The ending of the USMB increased doubts that
metricationMetrication refers to the introduction and use of the SI metric system, the international standard for physical measurements. This has involved a long process of independent and systematic conversions of countries from various local systems of weights and measures. Metrication began in France in...
would really be implemented. Public and private sector metrication slowed even while competitiveness between nations and demands of global marketplaces increased.
The ANMC was established in 1973 by the
American National Standards InstituteThe American National Standards Institute or ANSI is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organization also coordinates U.S. standards with international...
(ANSI) as a non-profit, tax-exempt organization for planning and coordinating metric activity in all sectors of the U.S. economy. The ANMC became a separately incorporated organization in 1976. The ANMC was intended to facilitate U.S. metrication by maintaining a voluntary and orderly process that minimizes costs and maximizes benefits, and to provide information, forums, individual assistance, and other services for its subscribers. The ANMC attempted to coordinate the metric planning of many industrial sectors, unlike the USMB, which only attempted to implement the policy set forth in the Metric Conversion Act of 1975. After the formation of the USMB, committees of the ANMC submitted conversion plans for the chemical sector and for the instruments sector. These sector conversion plans were later approved by the USMB. From 1975 through 1987, the ANMC held a series of well-attended annual conferences. Subsequently, a series of National Metric Conferences, jointly sponsored by the ANMC, the
U.S. Metric AssociationThe U.S. Metric Association , based in Northridge, California, is a non-profit organization that advocates for total conversion to the SI system in the United States ....
(USMA), the U.S. Department of Commerce, and the
National Institute of Standards and TechnologyThe National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory which is a non-regulatory agency of the United States Department of Commerce...
(NIST), were held from 1989 through 1993.
Congress included new encouragement for U.S. industrial metrication in the Omnibus Trade and Competitiveness Act of 1988. This legislation amended the Metric Conversion Act of 1975 and designated the metric system as "the Preferred system of weights and measures for United States trade and commerce". The legislation states that the Federal Government has a responsibility to assist industry, especially small business, as it voluntarily converts to the metric system of measurement.
This legislation required most federal agencies to use the metric system in their procurement, grants, and other business-related activities by the end of 1992. While not mandating metric use in the private sector, the Federal Government has sought to serve as a catalyst in the metric conversion of the country's trade, industry, and commerce. Exceptions were made for the highway and construction industries. The Department of Transportation planned to require metric units by 2000, but this plan was canceled by the
1998 highway bill TEA21The Transportation Equity Act for the 21st Century was enacted June 9, 1998, as Public Law 105-178. TEA-21 authorized the Federal surface transportation programs for highways, highway safety, and transit for the 6-year period 1998-2003...
. The U.S. military has generally high use of the metric system partly because of the need to work with other nations' militaries.
Some members of Congress attempted to ban use of the metric system on federal highways in 1992 and 1993. These bills were not popular in the House of Representives and failed before a vote.
Mars orbiter
The use of two different systems was the root cause in the loss of the
Mars Climate OrbiterThe Mars Climate Orbiter was one of two NASA spacecraft in the Mars Surveyor '98 program, the other being the Mars Polar Lander...
in 1998.
NASAThe National Aeronautics and Space Administration is an agency of the United States government, responsible for the nation's public space program. NASA was established by the National Aeronautics and Space Act on July 29, 1958, replacing its predecessor, the National Advisory Committee for...
specified metric units in the contract. NASA and other organizations worked in metric units, but one subcontractor,
Lockheed MartinLockheed Martin is a multinational aerospace manufacturer, global security and advanced technology company formed in 1995 by the merger of Lockheed with Martin Marietta. It is headquartered in Bethesda, Maryland, in the Washington Metropolitan Area. Lockheed Martin employs 146,000 people...
, provided thruster performance data to the team in pound force seconds instead of newton seconds. The spacecraft was intended to orbit
MarsMars is the fourth planet from the Sun in the Solar System. The planet is named after Mars, the Roman god of war. It is also referred to as the "Red Planet" because of its reddish appearance, due to iron oxide prevalent on its surface....
at about {{km to mi|150}} altitude, but the incorrect data meant that it probably descended instead to about {{km to mi|57}}, burning up in the Martian atmosphere.
Metrication efforts
The current effort toward national metrication is based on the claim that industrial and commercial productivity, mathematics and science education, and the competitiveness of U.S. products and services in world markets would be enhanced by completing the change to the international standard measurement system based on metric units. Gerard Iannelli, director of the U.S. Metric Program, gave the opinion that Americans have so far not adopted the Metric system because of the effort it takes to "translate" from Customary to Metric when both measurements are not available. He also cited what he perceived to be ineffective attempts at public education and awareness.
Daily life
While most people in the U.S. have studied metric units at school, metric usage remains low in daily life. Weather reports on television are given in
FahrenheitFahrenheit is the temperature scale proposed in 1724 by, and named after, the physicist Daniel Gabriel Fahrenheit . Today, the scale has been replaced by the Celsius scale in most countries; it is still in use for non-scientific purposes in the United States and a few other nations, such as...
and other customary units. Most speed limit and road signs are in miles per hour and miles. The
BTUThe British thermal unit is a traditional unit of energy. It is approximately the amount of energy needed to heat one pound of water one degree Fahrenheit. One Btu is equal to about 1.06 kilojoules. It is used in the power, steam generation, heating and air conditioning industries...
remains the common measure of heating and cooling, and clothing is measured in inches or sizes. Some of the more common
SI prefixAn SI prefix is a name or associated symbol that precedes a basic unit of measure to form a decimal multiple or submultiple. The abbreviation SI is from the French language name Système International d’Unités...
es are widely known, and are sometimes used with non-metric units. For example, computer memory storage capacity is measured in
kilobyteThe kilobyte is a unit of digital information storage equal to either 1,000 bytes or 1,024 bytes , depending on context....
s,
megabyteThe megabyte is an SI-multiple of the unit byte for digital information storage or transmission and is equal to 10
6 bytes. However, due to historical usage in computer-related fields it is still often used to represent 2
20 bytes. In rare cases, it is used to mean...
s, or
gigabyteThe gigabyte is an SI-multiple of the unit byte for digital information storage. The prefix giga means 109, therefore 1 gigabyte is ....
s. Nuclear explosions are measured in
kilotons and megatonsTNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is used as a unit of energy, approximately equivalent to the energy released in the detonation of this amount of TNT....
of
TNTTrinitrotoluene , or more specifically, 2,4,6-trinitrotoluene, is a chemical compound with the formula C
6H
23CH
3. This yellow-coloured solid is a reagent in chemistry but is best known as a useful explosive material with convenient handling properties...
. The letter
K is commonly used to denote "thousand" (e.g., "She ran a 5K race and earns $80K"). However, contrary to the SI system, this is often written with an uppercase
K instead of a lowercase
k. This usage has largely replaced the Roman numeral
M that was commonly used for "thousand" before the 1960s.
Consumer and retail
A number of U.S. consumer products come in rounded metric sizes. The trend seems to be toward more product sizes based on metric units, owing to the international nature of manufacturing, distribution, and sales. A few of these products display the metric quantity first or more prominently. Some items are produced and sold in rounded metric quantities (e.g., Crest Glide
dental flossDental floss is either a bundle of thin nylon filaments or a plastic ribbon used to remove food and dental plaque from teeth. The floss is gently inserted between the teeth and scraped along the teeth sides, especially close to the gums...
is available in 35, 40, and 50 meter packages).
Perhaps the most common metric item sold is the
two-liter bottleThe two-liter bottle is a common container for soft drinks. These bottles are produced from polyethylene terephthalate, also known as PET plastic, using the blow molding process. Bottle labels consist of a printed, tight-fitted plastic sleeve...
. Some
supermarketA supermarket, also called a grocery store in some parts of North America, is a self-service store offering a wide variety of food and household merchandise, organized into departments...
chains also make their
store brandStore brands or Private label brands in the United States, own brands in the UK, and home brands in Australia) are specific to retail stores or store chains...
soft drinks available in 3-liter sizes. Soft drink containers of 1 and 0.5 liters are sometimes sold alongside more popular 12 fl oz, 16 fl oz, 20 fl oz, and 24 fl oz (355, 473, 591, and 710 ml) sizes. Wine is also sold in standard bottles of 750 ml, as in the rest of the world. A fifth of liquor, once one fifth of a U.S. gallon, or 757 ml, is now commonly 750 ml, though it is still referred to as a 'fifth'. It is becoming increasingly common to find bottled water in half-liter and one-liter sizes, though 16 fl oz, 20 fl oz, and 24 fl oz sizes remain popular. However, attempts to sell 3- or 4-liter bottles of
milkMilk is an opaque white liquid produced by the mammary glands of mammals. It provides the primary source of nutrition for young mammals before they are able to digest other types of food. The early lactation milk is known as colostrum, and carries the mother's antibodies to the baby. It can reduce...
, instead of
gallonA gallon is a measure of volume of approximately four litres. Historically it has had many different definitions, but there are three definitions in current use. These are the U.S. liquid gallon and the lesser used U.S...
s (3.785 L), have been largely unsuccessful, and such bottles are almost never seen in the US.{{Citation needed|date=July 2009}}
Household products such as
shampooShampoo is a hair care product used for the removal of oils, dirt, skin particles, dandruff, environmental pollutants and other contaminant particles that gradually build up in hair...
,
mouthwashMouthwash or mouth rinse is a product used to enhance oral hygiene. Antiseptic and anti-plaque mouth rinse claim to kill the bacterial plaque causing caries, gingivitis, and bad breath. Anti-cavity mouth rinse uses fluoride to protect against tooth decay. But, it is generally agreed that the use...
, and
dental flossDental floss is either a bundle of thin nylon filaments or a plastic ribbon used to remove food and dental plaque from teeth. The floss is gently inserted between the teeth and scraped along the teeth sides, especially close to the gums...
have begun to be sold in metric sizes, and
PowerBarPowerBar is an American maker of energy bars and other related products ....
s and similar products have always been sold (but not marketed) by the gram. Consumer-size
photographic filmPhotographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and resolution of the film...
is commonly sold in a
35 mm standard35 mm film is the basic film gauge most commonly used for both still photography and motion pictures, and remains relatively unchanged since its introduction in 1892 by William Dickson and Thomas Edison, using film stock supplied by George Eastman. The photographic film is cut into strips...
(24x36 mm negative), although print sizes and
large formatLarge format describes large photographic films, large cameras, view cameras and processes that use a film or digital sensor, generally 4 x 5 inches or larger. The most common large formats are 4x5 and 8x10 inches...
films are defined in inches.{{Citation needed|date=July 2009}}
Sometimes metric and non-metric are combined on the same product. The standard method for
sizing tiresTire code or Tyre code - Automobile tires are described by an alphanumeric code, which is generally molded into the sidewall of the tire. This code specifies the dimensions of the tire, and some of its key limitations, such as load-bearing ability, and maximum speed...
combines millimeters for
treadThe tread of a tire or caterpillar track refers to the rubber on its circumference that makes contact with the road. As tires are used, the tread is worn down limiting their effectiveness in providing traction. A worn tire tread can be replaced using a process known as retreading. The word tread...
width but uses inches for rim
diameterIn geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...
. Tire inflation for a typical passenger car is 30
psi-As a letter or word:* Psi a letter of the Greek alphabet* Psi , a letter of the early Cyrillic alphabet, adopted from Greek-In science and technology:* Psi , a popular XMPP client program...
(pounds per square inch), which is also given in its metric equivalent (207 kPa, or Kilopascal). In
lightingLighting or illumination is the deliberate application of light to achieve some aesthetic or practical effect. Lighting includes use of both artificial light sources such as lamps and natural illumination of interiors from daylight. Daylighting is often used as the main source of light during...
, light bulbs use eighths of an inch for bulb diameter and full inches for fluorescent tube lengths, while the
socketSocket can refer to:In mechanics:* Socket wrench, a type of wrench that uses separate, removable sockets to fit different sizes of nuts and bolts...
is always in millimeters (for example, the standard "medium
EdisonThomas Alva Edison was an American inventor, scientist and businessman who developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and a long-lasting, practical electric light bulb...
screwA screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or a object that has the...
" is E26). On recently introduced
Christmas lightsThe use of decorative, festive lighting during the Christmas holiday season is a long standing tradition in many Christian cultures, and has been adopted as a secular practice in a number of other non-Christian, or non-predominantly Christian, cultures .While the use of celebratory lighting during...
, however, millimeters are often used with small
globeA globe is a three-dimensional scale model of Earth or other spheroid celestial body such as a planet, star, or moon...
-shaped bulbs (G30 and G40), and with miniature
LEDLEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
sets, where the standard T1¾ ({{frac|7|32}}-inch tube) ones are sometimes called M5 (5 mm miniature; not to be confused with
M5 threadThe ISO metric screw threads are the world-wide most commonly used type of general-purpose screw thread. They were one of the first international standards agreed when the International Organization for Standardization was set up in 1947.-Basic profile:...
).{{Citation needed|date=July 2009}}
Nutritional food labels typically report serving sizes in both systems but only list metric values (g or mg) for the breakdown of individual nutrients. The use of
CalorieThe calorie is a pre-SI metric unit of energy. The unit was first defined by Professor Nicolas Clément in 1824 as a unit of heat. This definition entered French and English dictionaries between 1841 and 1867. In most fields its use is archaic, having been replaced by the SI unit of energy, the joule...
s (large calorie) instead of kilo
jouleThe joule , named for James Prescott Joule, is the derived unit of energy in the International System of Units. It is the energy exerted by a force of one newton acting to move an object through a distance of one metre...
s is a case where a deprecated unit is used instead of the appropriate
SISi, si, or SI may refer to :- Places :* Mount Si, a mountain in state of Washington* Si County, county in Anhui, China* Si River, a river in China* Slovenia, a European nation Si, si, or SI may refer to (all SI unless otherwise stated):- Places :* Mount Si, a mountain in state of Washington* Si...
unit.
FPLA issues
Since 1992, the federal
Fair Packaging and Labeling ActThe Fair Packaging and Labeling Act is a US law that applies to labels on many consumer products. It requires the label to state:*The identity of the product;*The name and place of business of the manufacturer, packer, or distributor; and...
(FPLA) has required consumer goods to be labeled in both customary and metric units. There is a strong push by industry to amend this law to allow manufacturers to use metric-only labeling. Most states in the U.S. have already adopted laws allowing metric-only labeling. According to the European Community (now the
EUThe European Union is an economic and political union of 27 Member States, located primarily in Europe. Committed to regional integration, the EU was established by the Treaty of Maastricht on 1 November 1993 upon the foundations of the pre-existing European Economic Community...
) Directive 80/181/EEC issued on 20 December 1979, the European Union would have only allowed dual-unit labels to appear on products effective as of 31 December 2009, but problems experienced during metrication efforts in the UK forced the EU to abandon this deadline.
Pending the EU deadline, an amendment to the FPLA to allow metric-only labeling would allow manufacturers, both importers and exporters, to avoid the significant costs associated with having to produce two distinct types of package labels. A bill to permit metric-only labeling at the federal level was to have been introduced in 2005. Significant opposition from the
Food Marketing InstituteThe Food Marketing Institute is an organization that conducts food safety, public affairs, education, research, and industry relations programs for food retailers and wholesalers. FMI's membership consists of approximately 1,500 companies in 50 countries, ranging from large multi-chain stores to...
, representing U.S. grocers, has delayed the introduction of the bill. FMI expressed the fear that legislation to permit metric-only labels might also somehow mandate resizing of packaging to round metric sizes (a process already well underway), and this could require expensive remodeling or replacement of existing display cases. A compromise has been suggested whereby manufacturers in both the U.S. and the EU could opt for either metric-only or dual-unit labeling, but this idea has been viewed dimly by the EU negotiators.{{Citation needed|date=July 2009}}
Construction
Out of all industries, construction has adopted metric units least. Dimensional lumber comes in standard nominal inch cross-section sizes (e.g., a "2-by-4" is really 1½ by 3½ in). Lengths are given in feet.
Building codeA building code, or building control, is a set of rules that specify the minimum acceptable level of safety for constructed objects such as buildings and nonbuilding structures. The main purpose of the building codes is to protect public health, safety and general welfare as they relate to the...
s are established at the local level and the U.S. has extensive building standards that are based on customary units. Because of
CanadaCanada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean...
's proximity to the U.S., issues of common units still arise. This tendency in construction is similar to
Japanis an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, an otherwise metricated country, however traditional construction still uses
Japanese units' is the traditional Japanese system of measurement. The name shakkanhō originates from the name of two of the units, the shaku, a unit of length, and the kan, a mass measurement.The system is Chinese in origin...
predating metrication.
Aviation
Aircraft heights for air traffic control and related purposes are measured in feet in the U.S. In fact, most of the world continues to use feet for aviation altitudes, with the notable exceptions of China, North Korea, and Russia and many other
CIS{{Redirect|CIS}}{{Redirect|CIS}}{{Redirect|CIS}}{{Redirect|CIS}}{{Redirect|CIS}}{{Redirect|CIS}}{{Infobox Geopolitical organisation|native_name = Commonwealth of Independent States...
countries.
Education
Most students are taught the metric system in elementary, middle, and high school. Instruction primarily centers on the concepts of powers of 10, the associated prefixes, and the conversion from one prefix form to another. Units of length, volume, and mass are typically introduced through comparison with ordinary objects. The metric system is not reinforced much outside the classroom due to lack of popular metric usage. Consequently, while students may understand some of the concepts underlying the metric system, they do not necessarily have an intuitive sense of the value of the units.
In science education, students predominantly use metric measures in experiments and equations, allowing those interested in the sciences to become more familiar with the metric system. Science classes are requisites for undergraduate degree in the U.S. which ensures most educated people have some familiarity with the metric system. Within
higher educationHigher education refers to a level of education that is provided by universities, vocational universities, community colleges, liberal arts colleges, institutes of technology and other collegiate level institutions, such as vocational schools, trade schools and career colleges, that award academic...
, the metric system is universal for classes in the sciences (see below). Some non-science textbooks in the U.S. use only the metric system without giving conversions in order to promote metrication. Older students accustomed more to the U.S. customary units may be perplexed by unfamiliar metric measures.
Electricity and energy
There are no U.S. customary units for electric current, potential difference, or charge since these concepts were developed after the international adoption of metric in science. The metric units
ampereThe ampere is the SI unit of electric current. The ampere, in practice often shortened to amp, is an SI base unit, and is named after André-Marie Ampère, one of the main discoverers of electromagnetism....
,
voltThe volt is the SI derived unit of electromotive force, commonly called "voltage". It is also the unit for the related but slightly different quantity electric potential difference...
, and
coulombThe coulomb is the SI derived unit of electric charge. It is named after Charles-Augustin de Coulomb.- Definition :If 2 like point charges of equal magnitudes are placed in a vacuum at a distance of 1 metre away from each other and if they repel each other with a force of 9*1000000000 Newton, then...
have been the only units used. Energy is often measured in
watt-hourThe kilowatt hour, or kilowatt-hour, is a unit of energy equal to 3,600,000 joules.Energy in watt hours is the multiplication of power in watts and time in hours....
s, BTUs, or
calorieThe calorie is a pre-SI metric unit of energy. The unit was first defined by Professor Nicolas Clément in 1824 as a unit of heat. This definition entered French and English dictionaries between 1841 and 1867. In most fields its use is archaic, having been replaced by the SI unit of energy, the joule...
s rather than the SI
jouleThe joule , named for James Prescott Joule, is the derived unit of energy in the International System of Units. It is the energy exerted by a force of one newton acting to move an object through a distance of one metre...
. The rated power of engines,
electric motorAn electric motor uses electrical energy to produce mechanical energy, usually through the interaction of magnetic fields and current-carrying conductors. The reverse process, producing electrical energy from mechanical energy, is accomplished by a generator or dynamo. Traction motors used on...
s, and power plant
steam turbineA steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....
s is frequently described in
horsepowerHorsepower is the name of several non-SI units of power. It was originally defined to allow the output of steam engines to be measured and compared with the power output of draft horses. The horsepower was widely adopted to measure the output of piston engines, turbines, electric motors and other...
. Residential and commercial electrical energy use is metered and billed in kilowatt hours, kW·h, which is a measure of the
wattThe watt is a derived unit of power in the International System of Units . It measures rate of energy conversion. One watt is equivalent to 1 joule of energy per second....
s used over a period of time. Power plant output is generally expressed in millions of watts, or megawatts.
Heating, cooling, and combustion power are often measured in BTUs per hour. Fuel prices are mostly given in customary units, such as dollars per gallon, barrel, thousand cubic feet, or long ton . The SI term
hertzThe hertz is a unit of frequency. It is defined as the number of complete cycles per second. It is the basic unit of frequency in the International System of Units , and is used worldwide in both general-purpose and scientific contexts...
has replaced the term
cycles per second as a unit of frequency.
Financial services
The United States was one of the first nations to adopt decimal currency. Until 2001, U.S. stocks were traded in fractions of dollars (½, ¼, ⅛) based on the old Spanish
pieces of eightThe Spanish dollar is a silver coin, worth eight reales, that was minted in the Spanish Empire after a Spanish currency reform in 1497. It was legal tender in the United States until an Act of the United States Congress discontinued the practice in 1857...
. Some commodity market prices are quoted in customary units (such as barrels of oil,
troy ounceThe troy ounce is a unit of imperial measure. In the present day it is most commonly used to gauge the weight and therefore the price of precious metals....
s of gold, pounds of frozen pork bellies, etc.). The federal government reports international production figures in metric units (for instance, wheat in metric tons) but in bushels for domestic production figures.
Firearms
The U.S. continues to use the inch for
caliberThe term caliber designates the inside diameter of a tube, the diameter of a solid wire or rod, or a measurement of the length of a gun relative to its diameter....
on many civilian and law enforcement firearms. Except for the 9 mm, most widely recognizable calibers are in inches, such as the .45, .357, or .22. The arms industry is an international one, however, and many foreign gun manufacturers design, build, and sell firearms measured in inches (a good example is the
.357 SIGThe .357 SIG pistol cartridge is the product of Swiss firearms manufacturer SIG-Sauer, in cooperation with the American ammunition manufacturer Federal Cartridge. While it is based on a .40 S&W case necked down to accept bullets, the .357 SIG brass is longer...
caliber). Also, inch measurements of caliber may refer to the diameter of the bullet and not that of the barrel, like the .308 Winchester, which fires the same projectile as the
.30-06 SpringfieldThe .30-06 Springfield cartridge or 7.62 x 63 mm in metric notation, was introduced to the United States Army in 1906 and standardized, used until the 1960s and early 1970s. It replaced the .30-03, 6 mm Lee Navy and .30 US Army...
and the
.300 Savage.300 Savage cartridge is a rimless, .30 caliber rifle cartridge developed by the Savage Arms Company in 1920 which was designed to replace the less powerful .303 Savage in the their popular Savage Model 99 lever-action rifle...
. Often, the caliber is just a number close to the diameter of the bullet, like the
.220 SwiftThe .220 Swift is a rifle cartridge developed by Winchester and introduced in 1935. It was the first factory loaded rifle cartridge with a muzzle velocity of over 4,000 ft/s and is still one of the fastest and most accurate factory loaded small arms cartridges, though both the .17...
,
.223 RemingtonThe .223 Remington is a sporting cartridge with almost the same external dimensions as the 5.56x45mm NATO military cartridge. The name is pronounced either two-two-three or two-twenty-three...
and
.222 Remington MagnumThe .222 Remington Magnum was a short-lived commercially produced cartridge derived from the .222 Remington. Originally developed for a US prototype military rifle in 1958, the cartridge was not adopted by the military, but was introduced commercially in sporting rifles.-Development:The .222 Rem....
, all of which actually have .224 inch diameter bullets. The U.S. military, reflecting its need to ensure interoperability with its
NATOThe North Atlantic Treaty Organization ); ), also called "the Atlantic Alliance", is an intergovernmental military alliance based on the North Atlantic Treaty which was signed on April 4, 1949...
Allies, uses metric measurements for almost all weapons calibers, even when the caliber in question originated as or was derived from a different measurement. (e.g. 7.62 mm rather than
.308The .308 Winchester is a rifle round and is the commercial version of the military 7.62x51mm NATO centerfire cartridge. The .308 Winchester was introduced in 1952, two years prior to the NATO adoption of the 7.62x51mm NATO T65. Winchester branded the cartridge and introduced it to the commercial...
, or
5.56 mm5.56x45mm NATO is a rifle cartridge developed in the United States and originally chambered in the M16 rifle. Under STANAG 4172, it is a standard cartridge for NATO forces as well as many non-NATO countries. It is derived from, but not identical to, the .223 Remington cartridge...
instead of
.223The .223 Remington is a sporting cartridge with almost the same external dimensions as the 5.56x45mm NATO military cartridge. The name is pronounced either two-two-three or two-twenty-three...
).
Manufacturing
Globalization of manufacturing has led to wide adoption of metric standards, although this is not yet universal.
After a confusing period where
automobileAn automobile, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
s were assembled with both customary and metric
fastenerA fastener is a hardware device that mechanically joins or affixes two or more objects together.Fasteners can also be used to close a container such as a bag, a box, or an envelope; or they may involve keeping together the sides of an opening of flexible material, attaching a lid to a container,...
s in each vehicle, cars are now universally built with metric parts. Automobile engines, once named after their displacement in cubic inches, e.g. the 426 Hemi, are currently named after their rounded measurement in liters (e.g., the 6.1 L Hemi). Technical publications by industry publishers and American automakers often give engine displacements in both cubic inches and cubic centimeters (or liters). For example, the specifications for the Dodge SRT-8 6.1 L Hemi state the displacement as 370 cubic inches (6,059 cc).
The electronics and computer industries largely converted to metric standards as new technologies were introduced toward the end of the 20th century. Thus, while 5¼ inch
floppy diskA floppy disk is a data storage medium that is composed of a disk of thin, flexible magnetic storage medium encased in a square or rectangular plastic shell. Floppy disks are read and written by a floppy disk drive or FDD, the initials of which should not be confused with "fixed disk drive," which...
s were truly in 5¼ inch wide packages, the nominal design diameter of the replacement "3½ inch" disks was actually 90 mm.
CDA Compact Disc is an optical disc used to store digital data. It was originally developed to store sound recordings exclusively, but later it also allowed the preservation of other types of data. Audio CDs have been commercially available since October 1982...
s and
DVDDVD, also known as Digital Versatile Disc or Digital Video Disc,is an optical disc storage media format, and was founded in 1995. Its main uses are video and data storage...
s are 120 mm in diameter, but their size is rarely mentioned;
Mini CDMini CDs, or "Pocket" CDs are compact discs with a smaller form factor and half the capacity.-Formats:Amongst the various formats are the...
s are sometimes called "80 mm CDs". Computer fan sizes are exclusively referred to by metric units (120 mm or 80 mm case fans, for example), while
hard disk driveA hard disk drive is a non-volatile storage device that stores digitally encoded data on rapidly rotating platters with magnetic surfaces. Strictly speaking, "drive" refers to the motorized mechanical aspect that is distinct from its medium, such as a tape drive and its tape, or a floppy disk...
and CD drive bay widths are customary measurements, typically 3½ inches and 5¼ inches, respectively. Additionally, screen sizes are measured in inches, such as a 24-inch widescreen LCD.
Military
The U.S. military uses metric measurements extensively to ensure interoperability with allied forces, particularly
NATOThe North Atlantic Treaty Organization ); ), also called "the Atlantic Alliance", is an intergovernmental military alliance based on the North Atlantic Treaty which was signed on April 4, 1949...
STANAGSTANAG is the NATO abbreviation for Standardization Agreement, which set up processes, procedures, terms, and conditions for common military or technical procedures or equipment between the member countries of the alliance. Each NATO state ratifies a STANAG and implements it within their own military...
s, "standardization agreements". Ground forces measure distances in "
klickKlick is a common military term meaning kilometer when referring to distance. Its use became popular among US soldiers in Vietnam during the 1960s, although veterans of the war recall its usage as early as the 1950s. The term is of unknown origin...
s",
slangSlang is the use of highly informal words and expressions that are not considered standard in the speaker's dialect or language. It is often used as a way to say words that are not appropriate, and is not often found in the standard dictionary for the language...
for kilometers. Most military firearms are measured in metric units, beginning with the
M-14The M14 rifle, formally the United States Rifle, Caliber 7.62 mm, M14, is an American selective fire automatic rifle firing 7.62x51mm NATO ammunition. It was the standard issue US rifle until 1970...
which was introduced in 1957, although a few legacy exceptions exist, such as .50-
caliberThe term caliber designates the inside diameter of a tube, the diameter of a solid wire or rod, or a measurement of the length of a gun relative to its diameter....
guns. Aircraft ordnance is normally measured in pounds. Heavy weapon caliber is measured in millimeters. Military vehicles are generally built to metric standards. An exception is the U.S. Navy whose guns are measured in inches and whose undersea fleet measures distances in terms of "kiloyards" (equivalent to 914.4 m), depth as "feet", and velocity, in some cases, as "feet per second". The Navy and Air Force continue to measure distance in
nautical mileThe nautical mile is a unit of length corresponding approximately to one minute of arc of latitude along any meridian....
s and speed in
knotsThe knot is a unit of speed equal to one nautical mile per hour, which is equal to exactly 1.852 km/h and approximately 1.151 mph. The abbreviation kn is preferred by American and Canadian maritime authorities, and by the Institute of Electrical and Electronics Engineers; however, the...
; these units are now accepted for use with SI by the
BIPMThe International Bureau of Weights and Measures , is an international standards organization, one of three such organizations established to maintain the International System of Units under the terms of the Metre Convention...
.
Illegal drugs and controlled substances
Illegal drugs and controlled substances are often measured in metric quantities. The federal law prohibiting them defines the penalties in metric masses.
In everyday usage within its subculture, marijuana is sold using a combination of metric and American customary units. At small scales the basic unit is the gram (or fractions thereof), but for larger orders fractions of ounces and pounds are used generally starting at ⅛ ounce, which is often defined in turn as 3.5 grams and referred to simply as "an eighth." The term "kilo" is used quite commonly by those in law enforcement to describe the amount of drugs (in kilograms) seized during a drug bust. A kilo of illegal drugs (in particular
cocaineCocaine is a crystalline tropane alkaloid that is obtained from the leaves of the coca plant. The name comes from "coca" in addition to the alkaloid suffix -ine, forming cocaine. It is a stimulant of the central nervous system and an appetite suppressant...
) is often referred to by the slang term "key".
Science and medicine
In science, metric usage is essentially universal, consistent with worldwide usage, although additional specialized units are often utilized for specific purposes in various disciplines (such as the
light-yearAs defined by the International Astronomical Union , a light-year is the distance that light travels in a vacuum in one Julian year.The speed of light is 299,792,458 metres per second...
in
astronomyAstronomy is the scientific study of celestial objects and phenomena that originate outside the Earth's atmosphere...
). Medicine is generally metric, but where interaction with patients is required, usage is often mixed. Doctors often measure a patient's weight in pounds to compute a dosage of medicine administered in grams or milliliters. Heights are measured in inches but head circumferences in centimeters. Even in many cases for which metric units are otherwise used, U.S. practice often varies from the rest of the world. For example, U.S. diabetes patients measure their
blood sugarBlood sugar concentration, or glucose level, refers to the amount of glucose present in the blood of a human or animal. Normally, in mammals the blood glucose level is maintained at a reference range between about 3.6 and 5.8 mM...
levels in milligrams per deciliter, whereas most other countries use
millimolesThe mole is a unit of amount of substance: it is an SI base unit, and one of the few units used to measure this physical quantity. The name "mole" was coined in German by Wilhelm Ostwald in 1893, although the related concept of equivalent mass had been in use at least a century earlier...
per liter.
In hospital settings, patient data is typically recorded using metric quantities, but all interaction with patients is done with reference to U.S. customary units (i.e., patient weights might be recorded in kilograms but discussed with patients in pounds). Because of online access to BMI calculators and concern over rising obesity rates, the international standard of
body mass indexThe body mass index , or Quetelet index, is a controversial statistical measurement which compares a person's weight and height. Though it does not actually measure the percentage of body fat, it may be a useful tool to estimate a healthy body weight based on how tall a person is...
based on the relationship between weight in kilograms and height in meters has been widely adopted by American healthcare workers and patients.
Meteorologists are required to have substantial knowledge of the metric system, since most observing, analysis, synoptic weather charts, and computer forecast models are all done in metric. Because most weather forecasts are issued to the public in customary units, meteorologists must also know how to convert between the two systems.
Usage among veterinarians varies, but because of the heavy emphasis on public interaction, animal weights (e.g., for cats or dogs) are nearly always recorded and reported in pounds and ounces. Usage at veterinary teaching hospitals, by contrast, favors the SI units.
In early 2007, NASA announced that it will use metric units for all operations on the lunar surface when it returns to the Moon, projected for 2020.
Sports
U.S. citizens are frequently exposed to metric units through coverage of international sporting events, particularly the
Olympic GamesThe Olympic Games are a major international event of summer and winter sports, in which thousands of athletes compete in a wide variety of events. The Games are currently held every two years, with Summer and Winter Olympic Games alternating. Originally, the ancient Olympic Games were held in...
.
Races in the U.S. are usually run in metric distances (e.g., the 100 meter dash and 5 km ("5K") races), although the mile distance remains popular. Note, however, particularly for local events, even a "5K" race is often promoted as a "3.1-mile" event, and the course markers will be at one-mile (not one kilometer) intervals. The marathon is referred to as a 26-mile race (actually 26.22 miles) rather than 42.195 km.
Measured distances as used in events such as
shot putThe shot put is an athletics event involving "putting" a heavy metal ball as far as possible...
,
high jumpThe high jump is a track and field athletics event in which competitors must jump over a horizontal bar placed at measured heights without the aid of any devices. It has been contested since the Olympic Games of ancient Greece. Over the centuries since, competitors have introduced increasingly more...
, and
discus throwThe discus throw is an event in track and field competition, in which an athlete throws a heavy disc — called a discus — in an attempt to mark a farther distance than his or her competitors. It is an ancient sport, as evidenced by the 5th century BC Myron statue, Discobolus...
are, however, often in feet and inches, except at the national and international levels. The field and court sizes for most popular team sports (even
soccerAssociation football, more commonly known as football or soccer, is a team sport played between two teams of eleven players using a spherical ball...
) were originally set in non-metric units. This is reflected in
American footballAmerican football, known in the United States and Canada simply as football, and often as Gridiron or Tackle football outside North America, is a competitive team sport known for combining strategy with physical play. The objective of the game is to score points by advancing the ball into the...
, in which the playing field is divided into yards, and many important statistics are measured in yards. Some sporting equipment, such as
skiA ski is a long, flat device worn on the feet designed to help the wearer slide smoothly over snow. Originally intended as an aid to travel in snowy regions, they are now primarily used for recreational and sporting purposes...
s and
polesSki Stocks are used by skiers to improve balance, speed and acceleration. They probably evolved from walking sticks carried while traveling, and possibly from spears as well....
, is sold in metric units. The lengths of automobile and horse races in the U.S. are generally set in miles.
Bicycles, especially at the high end, are increasingly being sold and sized in metric (for example, a frame described as "21 inch" size in the past is now often labeled as a "53 cm" frame instead). Some bicycle wheels are labeled in metric as "700c" for a nominal 700 mm diameter road bike tire, but mountain bikes tend to use 26-inch wheels.
Common
swimming poolA swimming pool, swimming bath, wading pool, or simply a pool, is an artificially enclosed body of water intended for swimming or water-based recreation. There are many standard sizes; the largest and deepest is the Olympic size...
dimensions are 25-yard, 25-meter, and 50-meter. High schools and the NCAA conduct 25-yard competitions.
USA SwimmingUSA Swimming is the national governing body for competitive swimming in the United States. It is charged with selecting the United States Olympic Swimming team and any other teams which officially represent the United States, as well as the overall organization and operation of the sport within the...
(USA-S) swims in both metric and non-metric pools.
Transportation
Highway speed limits are posted in miles per hour and distances are largely displayed in miles, yards, or feet, although a few dual mile/km signs can be found, mostly left over from demonstration projects that are no longer supported. One exception is
Interstate 19Interstate 19 is an intrastate Interstate Highway located entirely within the state of Arizona. I-19 runs from Nogales, at the Mexican border to Tucson, at Interstate 10.-Route description:...
in Arizona, because of its direct link to
MexicoThe United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
,{{Citation needed|date=June 2009}} which is almost completely signed in metric, except for speed limit signs. Signage on this road is, however, being converted back to customary units as they are replaced. Another exception is the turnpike section of
Delaware Highway 1Delaware Route 1 is a 103.02 mile long, four-to-six lane highway going from the Maryland-Delaware line on the eastern Atlantic shoreline to the Delaware Turnpike outside of Wilmington....
, which uses a kilometer-based system, in anticipation of the mid-1990s conversion in the U.S. to the metric system (which did not happen). Distances were originally signed in kilometers, but have since been replaced with standard milemarkers. The exit signs have remained metric.
Since 2000, the
Manual on Uniform Traffic Control DevicesThe Manual on Uniform Traffic Control Devices is a document issued by the Federal Highway Administration of the United States Department of Transportation to specify the standards by which traffic signs, road markings , and signals are designed, installed, and used...
has been published in both metric and American Customary Units. Metric signs, including speed signs in kilometers per hour, are now displayed in the manual even though they are not normally used on the roads and there is no definite plan to go metric yet. For visual distinction, regulatory and advisory metric speed signs have black circles around the numbers followed by "km/h" and other regulatory metric signs have yellow plates reading "METRIC" in black on top of the main signs. Officially, this means that, although not widely used, metric road signs are
allowed in the United States. The
UK Metric AssociationThe UK Metric Association, or UKMA, is an advocacy group in the United Kingdom that argues for completion of the British metrication programme...
considers this one way in which metrication is ahead of the United Kingdom, where metric road signs are usually illegal.
Due to their proximity to
CanadaCanada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean...
, the states of
WashingtonWashington is a state in the Pacific Northwest region of the United States. Washington was carved out of the western part of Washington Territory which had been ceded by Britain in 1846 by the Oregon Treaty as settlement of the Oregon Boundary Dispute. It was admitted to the Union as the...
,
VermontThe State of Vermont is a state in the New England region of the northeastern United States of America. The state ranks 43rd by land area, , and 45th by total area. It has a population of 621,270, making it the second least-populated state...
,
New HampshireNew Hampshire is a state in the New England region of the northeastern United States of America. The state was named after the southern English county of Hampshire. It borders Massachusetts to the south, Vermont to the west, Maine and the Atlantic Ocean to the east, and the Canadian province of...
,
MaineThe State of Maine is a state in the New England region of the northeastern United States, bordering the Atlantic Ocean to the southeast, New Hampshire to the southwest, and the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast. Maine is the northernmost portion of...
, and parts of
Upstate New YorkUpstate New York is the region of New York State north of the core of the New York metropolitan area.-Definition:There is no clear or official boundary between Upstate New York and Downstate New York, but the term "Upstate" is sometimes used to refer to the whole of the state besides New York City...
include distances in both miles and kilometers on many highway signs,{{Citation needed|date=January 2009}} especially in municipalities close to the border, although some older signs still have miles only. Newer signs on state highways on the island of
Kaua‘iKauai or Kauai is the oldest of the main Hawaiian Islands. With an area of , it is the fourth largest of the main islands in the Hawaiian archipelago and the 21st largest island in the United States...
in
Hawai‘iHawaii is the newest of the 50 U.S. states, and is the only state made up entirely of islands. It is located on an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of Australia. The state was admitted to the Union on August...
also include distances in both miles and kilometers. Mile markers along highways on the Island of Hawai'i will indicate both units whenever the
whole kilometer corresponds with the
whole mile (ex.: 5mi/8 km). At least one route (U.S. Route 31) in Alabama has both mileposts and kilometer-posts.{{Citation needed|date=February 2008}} In Houston, Texas many speed limits have km/h signs underneath the MPH signs. These are located near both airports and in the Texas Medical Center. The U.S. territory of
Puerto RicoPuerto Rico , officially the Commonwealth of Puerto Rico , is a self-governing unincorporated territory of the United States located in the northeastern Caribbean, east of the Dominican Republic and west of the Virgin Islands...
generally uses American-style (
MUTCDThe Manual on Uniform Traffic Control Devices is a document issued by the Federal Highway Administration of the United States Department of Transportation to specify the standards by which traffic signs, road markings , and signals are designed, installed, and used...
) signs with metric measurement on highways, displaying kilometer posts and distances in km, yet speed limit signs are in miles per hour.
Gasoline and diesel fuel are sold by the U.S. gallon, and
fuel economyFuel usage in automobiles refers to the relationship between distance traveled by an automobile and the amount of fuel consumed. There are no quantities or units for fuel usage defined in the International Standard ISO 31 Quantities and Units, so the nationally-defined reciprocal quantities fuel...
is rated in miles per gallon (MPG). However, some border towns neighboring Canada display the equivalent cost in Canadian dollars per liter because of the many Canadians who cross the border to buy cheaper gasoline.{{Citation needed|date=February 2007}} Automobile crankcase oil is sold by the quart, antifreeze by the gallon, and brake fluid and A/C refrigerant by the fluid ounce. Windshield wiper replacement blades are measure in inches.
Domestic airline flights are assigned altitudes in feet and measure speed in
knotsThe knot is a unit of speed equal to one nautical mile per hour, which is equal to exactly 1.852 km/h and approximately 1.151 mph. The abbreviation kn is preferred by American and Canadian maritime authorities, and by the Institute of Electrical and Electronics Engineers; however, the...
.
Nautical chartA nautical chart is a graphic representation of a maritime area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land , natural features of the seabed, details of the coastline, navigational hazards, locations of natural and man-made aids...
s show depth in
fathomA fathom is a unit of length in the Imperial system , used especially for measuring the depth of water.There are 2 yards in a fathom...
s and use the
nautical mileThe nautical mile is a unit of length corresponding approximately to one minute of arc of latitude along any meridian....
for distance. (One minute of arc of latitude at the radius of the earth at sea level was the standard for one nautical mile until ca. 1929. The nautical mile is now defined as exactly 1852 meters.) Railroads use the
standard gaugeThe standard gauge is a widely-used rail gauge. Approximately 60% of the world's existing railway lines are built to this gauge...
of 4 feet 8½ inches, as does most of Europe (where it is expressed instead as 1435 mm). U.S. Federal Motor Vehicle Safety Standard 101, which governs vehicle controls and displays, permit speedometers to display miles per hour, kilometers per hour, or both. Odometers are permitted to record miles or kilometers, but must be clearly labeled as to which unit they record. In practice, virtually all U.S.-market vehicles have mile odometers and dual labeled speedometers with mile-per-hour as the primary calibration. Some vehicles with electronic speed and distance readouts can be switched between U.S. and metric units.
Hybrid units
Some measurements are done in units derived from both customary and metric units. For example:
- Power per unit length from a nuclear reactor fuel rod: kilowatts per foot
- Heat rate from a power plant: BTUs per hour per kilowatt
- Federal automobile exhaust emission standards: grams per mile
- Caffeine in beverages: milligrams per ounce
- Running load limits specified in Boeing airplane flight manuals: kilograms per inch.
- Energy Efficiency Ratio (EER), which is the ratio of an air conditioner's cooling capacity in BTU/hr and its input power in watts. It is used instead of the coefficient of performance
The coefficient of performance or COP , of a heat pump is the ratio of the change in heat at the "output" to the supplied work.- Equation :The equation is:where...
, which is a dimensionless ratio that is the same in any system of units as long as they are consistent.
Any measurement that combines customary units with electrical units is necessarily hybrid, since there are no U.S. customary electrical units. An example can be found in Table 8, chapter 9 of the
National Electrical Code Handbook (8th ed.) where resistance of conductors per unit length is given in ohms per thousand feet.
Other units are based on customary units but use metric prefixes. For example, distance to target for a U.S. submarine is expressed in kiloyards.
Cultural impact
The continuing usage of U.S. customary units has been a cause for speculation in fiction set in the future. Many such works of fiction have assumed that the United States and the human race in general will use metric units in the future; however, others have considered the continuing persistence of the U.S. customary system to be more likely. Additionally, writers will sometimes use customary units simply because American readers and watchers will understand the measurements; other times, they are simply used by accident. The 1966 show
Star TrekStar Trek is a science fiction television series created by Gene Roddenberry that aired from September 8, 1966 to September 2, 1969. Though the original series was titled simply Star Trek, it has acquired the retronym Star Trek: The Original Series to distinguish it from the spinoffs that...
, for instance, initially used U.S. customary units despite multiple Earth national origins and a setting in the 23rd century. Later, starting with "
The Changeling"The Changeling" is a season two episode of Star Trek: The Original Series, first broadcast on September 29, 1967 and repeated May 17, 1968. It is episode #32, production #37 and was written by John Meredyth Lucas, and directed by Marc Daniels....
", metric measures were used, albeit inconsistently. Later sequels to the show, such as
Star Trek: The Next GenerationStar Trek: The Next Generation is a science fiction television series created by Gene Roddenberry as part of the Star Trek franchise. Created about 21 years after the original Star Trek, and set in the 24th century about 80 years after the orginal series, the program features a new crew and a new...
, used the metric system exclusively.
Both the metric system and attitudes in the U.S. toward the metric system are a target of humorous jabs in shows such as
The SimpsonsThe Simpsons is an American animated television sitcom created by Matt Groening for the Fox Broadcasting Company. The series is a satirical parody of a middle class American lifestyle epitomized by its eponymous family, which consists of Homer, Marge, Bart, Lisa, and Maggie...
and
FuturamaFuturama is an animated American sci-fi sitcom created by Matt Groening and developed by Groening and David X. Cohen for the Fox network. The series follows the adventures of a late 20th-century New York City pizza delivery boy, Philip J...
{{Citation needed|date=September 2009}}. The
Saturday Night LiveSaturday Night Live is a weekly late-night sketch comedy and variety show filmed in New York City. It made its debut on October 11, 1975, under a slightly different title. The show features a regular cast of comedy actors, joined by a guest host and musical act...
sketch
DecabetThe Decabet was a Saturday Night Live sketch in which Mr. Joseph Franklin of the U.S. Council of Standards and Measures introduces the new "metric alphabet"-the "Decabet". It originally aired on April 24, 1976 ....
, released in the height of the metrication movement, lampooned the different metric measurements by introducing a new Metric Alphabet consisting of only ten letters.
See also
- Plan for Establishing Uniformity in the Coinage, Weights, and Measures of the United States, 1790 report including proposal for decimal system based on the foot
- The Metric Marvels
The Metric Marvels is a series of seven animated educational shorts featuring songs about meters, liters, Celsius, and grams, designed to teach American children how to use the metric system. They were produced by Yohe & Newall, the same advertising agency which produced ABC's popular Schoolhouse...
- Metrication controversy
External links
{{Metrication}}
{{DEFAULTSORT:Metrication In The United States}}