Metrication in the United States - AbsoluteAstronomy.com

Metrication 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...

is the process of introducing the International System of Units

International System of Units

The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

(SI or Système International), a metric system

Metric system

The metric system is an international decimalised system of measurement. France was first to adopt a metric system, in 1799, and a metric system is now the official system of measurement, used in almost every country in the world...

of measurement, to replace the historical or customary units of measurement of a country or region. The United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

does not officially use or mandate a metric system of units, making it one of only three countries, along with Burma (Myanmar) and Liberia

Liberia

Liberia , officially the Republic of Liberia, is a country in West Africa. It is bordered by Sierra Leone on the west, Guinea on the north and Côte d'Ivoire on the east. Liberia's coastline is composed of mostly mangrove forests while the more sparsely populated inland consists of forests that open...

, that still use customary units.

19th century

In the early 19th century, the U.S. Coast and Geodetic Survey (the government's surveying and map-making agency) used meter and kilogram

Kilogram

The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...

standards brought from France

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

. In 1866, Congress

United States Congress

The United States Congress is the bicameral legislature of the federal government of the United States, consisting of the Senate and the House of Representatives. The Congress meets in the United States Capitol in Washington, D.C....

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 Order

Mendenhall Order

The 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 General Conference on Weights and Measures

General Conference on Weights and Measures

The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures . It is one of the three organizations established to maintain the International System of Units under the terms of the Convention du Mètre of 1875...

is the governing body for the modern metric system and comprises the signing nations of the Treaty of the Meter. The General Conference on Weights and Measures approved an updated version of the metric system in 1960 named Le Système international d'unités (International System of Units) and abbreviated SI
Si
Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...

.

On February 10, 1964, the National Bureau of Standards (former name of National Institute of Standards and Technology

National Institute of Standards and Technology

The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...

) issued a statement that it will use the metric system:

The metrication of the United Kingdom and the other Commonwealth nations

Commonwealth of Nations

The Commonwealth of Nations, normally referred to as the Commonwealth and formerly known as the British Commonwealth, is an intergovernmental organisation of fifty-four independent member states...

, particularly Canada

Metrication in Canada

Canada has converted to the metric system for many purposes but there is still significant use of non-metric units and standards in many sectors of the Canadian economy...

, increased the need for 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 its 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 1975

Metric Conversion Act

The 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. 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 Reagan

Ronald Reagan

Ronald Wilson Reagan was the 40th President of the United States , the 33rd Governor of California and, prior to that, a radio, film and television actor....

administration to reduce federal spending, the USMB was disbanded in autumn of 1982.

The ending of the USMB increased doubts that metrication

Metrication

would really be implemented. Public and private sector metrication slowed even while competitiveness between nations and demands of global marketplaces increased.

The American National Metric Council (ANMC) was established in 1973 by the American National Standards Institute

American National Standards Institute

The American National Standards Institute 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 Association

U.S. Metric Association

The 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 Technology

National Institute of Standards and Technology

(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 TEA21

Transportation Equity Act for the 21st Century

The 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 Representatives and failed before a vote.

Mars orbiter

The use of two different unit systems was the cause of the loss of the Mars Climate Orbiter

Mars Climate Orbiter

The Mars Climate Orbiter was a 338 kilogram robotic space probe launched by NASA on December 11, 1998 to study the Martian climate, atmosphere, surface changes and to act as the communications relay in the Mars Surveyor '98 program, for Mars Polar Lander...

in 1998. NASA

NASA

The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

specified metric units in the contract. NASA and other organizations applied metric units in their work, but one subcontractor, Lockheed Martin

Lockheed Martin

Lockheed Martin is an American global aerospace, defense, security, and advanced technology company with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta in March 1995. It is headquartered in Bethesda, Maryland, in the Washington Metropolitan Area....

, provided thruster performance data to the team in pound force seconds instead of newton seconds. The spacecraft was intended to orbit Mars

Mars

Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

at about 150 kilometres (93.2 mi) altitude, but incorrect data probably caused it to descend instead to about 57 kilometres (35.4 mi), burning up in the Martian atmosphere.

Metrication efforts

The effort toward national metrication is based on the premise that the U.S. industrial and commercial productivity, mathematics and science education, and the competitiveness of its products and services in world markets would be enhanced by the adoption of the metric system. Gerard Iannelli, director of the U.S. Metric Program, gave the opinion that Americans have so far not done so because of the effort it takes to "translate" from customary to metric units when both measurements are not shown. He also cited what he perceived to be ineffective attempts at public education and awareness.

Daily life

While most Americans have studied metric units at school, metric usage remains low in daily life. Speed limits are almost always in miles per hour and road signs usually give distances in miles or feet. The BTU

British thermal unit

The British thermal unit is a traditional unit of energy equal to about 1055 joules. It is approximately the amount of energy needed to heat of water, which is exactly one tenth of a UK gallon or about 0.1198 US gallons, from 39°F to 40°F...

remains the common measure of heating and cooling, and clothing is measured in inches. Some of the more common SI prefix

SI prefix

The International System of Units specifies a set of unit prefixes known as SI prefixes or metric prefixes. An SI prefix is a name that precedes a basic unit of measure to indicate a decadic multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol...

es are widely known, and are sometimes used with non-metric units. For example, computer memory storage capacity is measured in kilobyte

Kilobyte

The kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...

s, megabyte

Megabyte

The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...

s, or gigabyte

Gigabyte

The gigabyte is a multiple of the unit byte for digital information storage. The prefix giga means 109 in the International System of Units , therefore 1 gigabyte is...

s. Nuclear explosions are measured in kilotons and megatons

TNT equivalent

TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...

of TNT. The letter K is commonly used to denote "thousand" (e.g., "She 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; in fact, the "M" has now come to denote "million" (e.g., "$32.5M budget").

Weather

Televised weather reports are given in Fahrenheit

Fahrenheit

Fahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...

for dew point and air temperatures, miles per hour for windspeed, inches of mercury or millibars for atmospheric pressure

Atmospheric pressure

Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

, and other customary units. In some states on the Canadian border such as Washington (State), Michigan

Michigan

Michigan is a U.S. state located in the Great Lakes Region of the United States of America. The name Michigan is the French form of the Ojibwa word mishigamaa, meaning "large water" or "large lake"....

and New York

New York

New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...

, temperatures are described in both Fahrenheit and Celsius, as the broadcasts can be received in Vancouver, Canada and Ontario, Canada, which uses Celsius.

Consumer and retail

Some U.S. consumer products come in rounded metric sizes. This appears to be increasing because of the international nature of manufacturing, distribution, and sales. A few products display the metric quantity first or more prominently. Some items are produced and sold in rounded metric quantities (e.g., Crest Glide dental floss

Dental floss

Dental floss is made of 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. Dental floss may be flavored or unflavored, and...

is available in 35-, 40-, and 50-meter packages).

Perhaps the most common metric item sold is the two-liter bottle

Two-liter bottle

The 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 supermarket

Supermarket

A supermarket, a form of grocery store, is a self-service store offering a wide variety of food and household merchandise, organized into departments...

chains also make their store brand

Store brand

Store brands are a line of products sold by a retailer under a single marketing identity. They bear a similarity to the concept of House brands, Private label brands in the United States, own brands in the UK, and home brands in Australia and generic brands...

soft drinks available in 3-liter sizes. Soft drink containers of 1 and 0.5 liters are sometimes sold alongside 12 fl oz

Fluid ounce

A fluid ounce is a unit of volume equal to about 28.4 mL in the imperial system or about 29.6 mL in the US system. The fluid ounce is distinct from the ounce, which measures mass...

, 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 jugs of milk

Milk

Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...

, instead of gallon

Gallon

The gallon is a measure of volume. Historically it has had many different definitions, but there are three definitions in current use: the imperial gallon which is used in the United Kingdom and semi-officially within Canada, the United States liquid gallon and the lesser used United States dry...

s (3.785 L), have been largely unsuccessful, and such bottles are almost never seen in the US.

Household products such as shampoo

Shampoo

Shampoo 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...

, mouthwash

Mouthwash

Mouthwash or mouth rinse is a product used to enhance oral hygiene. Some manufacturers of mouthwash claim that antiseptic and anti-plaque mouth rinse kill the bacterial plaque causing cavities, gingivitis, and bad breath. Anti-cavity mouth rinse uses fluoride to protect against tooth decay...

, and dental floss

Dental floss

have begun to be sold in metric sizes, and PowerBar

PowerBar

PowerBar 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 film

Photographic film

Photographic 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 standard

35 mm film

35 mm film is the film gauge most commonly used for chemical still photography and motion pictures. The name of the gauge refers to the width of the photographic film, which consists of strips 35 millimeters in width...

(24x36 mm negative), although print sizes and large format

Large format

Large format refers to any imaging format of 4×5 inches or larger. Large format is larger than "medium format", the 6×6 cm or 6×9 cm size of Hasselblad, Rollei, Kowa, Pentax etc cameras , and much larger than the 24×36 mm frame of 35 mm format.The main advantage...

films are defined in inches. Digital camera sensor sizes are measured in an archaic manner indicating inverse fractions of an inch, as a 1/1.6" sensor is larger than 1/2.5" sensor.

Sometimes metric and non-metric are combined on the same product. The standard method for sizing tires

Tire code

Automobile tires are described by an alphanumeric tire code or tyre 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 tread

Tread

The tread of a tire or track refers to the rubber on its circumference that makes contact with the road. As tires are used, the tread is worn off, limiting its effectiveness in providing traction. A worn tire tread can often be retreaded. The word tread is often used incorrectly to refer to the...

width but uses inches for rim diameter

Diameter

In 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

Pounds per square inch

The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...

(pounds per square inch), which is also given in its metric equivalent (207 kPa, or Kilopascals). In lighting

Lighting

Lighting or illumination is the deliberate application of light to achieve some practical or aesthetic effect. Lighting includes the use of both artificial light sources such as lamps and light fixtures, as well as natural illumination by capturing daylight...

, light bulbs

Incandescent light bulb

The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...

use eighths of an inch for bulb diameter and full inches for fluorescent tube lengths, while the socket

Jack (connector)

In electronics and electrical assemblies, the term jack commonly refers to a surface-mounted connector, often, but not always, with the female electrical contact or socket, and is the "more fixed" connector of a connector pair...

is always in millimeters (for example, the standard "medium Edison screw

Edison screw

The Edison screw fitting is a system of connectors used for light bulbs, developed by Thomas Edison and licensed starting in 1909 under the Mazda trademark. Most have a right-hand threading, so that it goes in when turned clockwise and comes out when turned counterclockwise, like a hardware screw...

" is E26). On recently introduced Christmas lights, however, millimeters are often used with small globe

Globe

A 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 LED

LEd

LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....

sets, where the standard T1¾ (-inch tube) ones are sometimes called M5 (5 mm miniature; not to be confused with M5 thread

ISO metric screw thread

The 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:...

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 Calorie

Calorie

The calorie is a pre-SI metric unit of energy. It was first defined by Nicolas Clément in 1824 as a unit of heat, entering 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 kilojoule

Joule

The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...

s is a case where a deprecated unit (itself invented as a metric version of the BTU) is used in place of the appropriate SI

Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...

unit.

FPLA issues

Since 1992, the federal Fair Packaging and Labeling Act

Fair Packaging and Labeling Act

The 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. Some industries are engaged in efforts to amend this law to allow manufacturers to use only metric labeling. Forty-eight U.S. states have adopted laws permitting labeling in metric units only with the two exceptions being New York and Alabama. New York is reportedly examining a shift to allow metric labeling According to the European Community (now the EU

European Union

The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

) Directive 80/181/EEC issued on December 20, 1979, the European Union would have only allowed dual-unit labels to appear on products until December 31, 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 Institute

Food Marketing Institute

The 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.

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 inches). Lengths are given in feet. Building code

Building code

A 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 building codes are 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 Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends 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 Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, 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 where traditional construction still uses Japanese units

Japanese units of measurement

' 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 use feet for aviation altitudes after the end of WW2 (in meters before 1945 in all European countries except GB), with the notable exceptions of China, North Korea, Russia and many other CIS

Commonwealth of Independent States

The Commonwealth of Independent States is a regional organization whose participating countries are former Soviet Republics, formed during the breakup of the Soviet Union....

(former Soviet) countries. For instance, an airliner on a long flight, even if neither its starting point nor destination are in the United States, might use a cruising altitude of an even 36,000 feet, rather than an even 10,000 meters.

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 education

Higher education

Higher, post-secondary, tertiary, or third level education refers to the stage of learning that occurs at universities, academies, colleges, seminaries, and institutes of technology...

, 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.

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 ampere

Ampere

The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...

, volt

Volt

The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...

, ohm

Ohm

The ohm is the SI unit of electrical resistance, named after German physicist Georg Simon Ohm.- Definition :The ohm is defined as a resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere,...

and coulomb are the only units used. The SI term hertz

Hertz

The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....

has replaced the term cycles per second as a unit of frequency.

Energy is often measured in watt-hour

Watt-hour

The kilowatt hour, or kilowatt-hour, is a unit of energy equal to 1000 watt hours or 3.6 megajoules.For constant power, energy in watt hours is the product of power in watts and time in hours...

s, BTUs, therm

Therm

The therm is a non-SI unit of heat energy equal to 100,000 British thermal units . It is approximately the energy equivalent of burning 100 cubic feet of natural gas....

s or calorie

Calorie

s rather than the SI joule

Joule

. Residential and commercial electrical energy use is metered and billed in kilowatt hours, kW·h. Fuel prices are mostly given in customary units, such as dollars per gallon, barrel, thousand cubic feet, or ton (short or long). Heating, cooling, and combustion power are often measured in BTUs per hour. The rated power of engines, electric motor

Electric motor

An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

s, and power plant steam turbine

Steam turbine

A 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 horsepower

Horsepower

Horsepower is the name of several units of measurement of power. The most common definitions equal between 735.5 and 750 watts.Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the...

. Power plant output is generally expressed in megawatts.

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 eight

Spanish dollar

The Spanish dollar is a silver coin, of approximately 38 mm diameter, worth eight reales, that was minted in the Spanish Empire after a Spanish currency reform in 1497. Its purpose was to correspond to the German thaler...

, but the Securities and Exchange Commission ordered stocks to transition to dollars and cents to better integrate with global markets. Some commodity market prices are quoted in customary units (such as barrels of oil, troy ounce

Troy ounce

The troy ounce is a unit of imperial measure. In the present day it is most commonly used to gauge the weight of precious metals. One troy ounce is nowadays defined as exactly 0.0311034768 kg = 31.1034768 g. There are approximately 32.1507466 troy oz in 1 kg...

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 caliber

Caliber

In guns including firearms, caliber or calibre is the approximate internal diameter of the barrel in relation to the diameter of the projectile used in it....

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 SIG

.357 SIG

The .357 SIG pistol cartridge is the product of Swiss-German 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 slightly longer...

cartridge, which is actually a 9 mm 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 Springfield

.30-06 Springfield

The .30-06 Springfield cartridge or 7.62×63mm in metric notation, was introduced to the United States Army in 1906 and standardized, and was in use 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

The .300 Savage cartridge is a rimless, .30 caliber rifle cartridge developed by the Savage Arms Company in 1920. It was designed to replace the less powerful .303 Savage in 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 Swift

.220 Swift

The .220 Swift is a semi-rimmed rifle cartridge developed by Winchester and introduced in 1935. It was the first factory loaded rifle cartridge with a muzzle velocity of over...

, .223 Remington

.223 Remington

The .223 Remington is a sporting cartridge with almost the same external dimensions as the 5.56×45mm NATO military cartridge. The name is commonly pronounced either two-two-three or two-twenty-three. It is loaded with a diameter, jacketed bullet, with weights ranging from , though the most common...

and .222 Remington Magnum

.222 Remington Magnum

The .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 0.224 inches (5.7 mm) bullets. The U.S. military, reflecting its need to ensure interoperability with its NATO 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 .308

.308 Winchester

The .308 Winchester is a rifle cartridge and is the commercial cartridge upon which the military 7.62x51mm NATO centerfire cartridge is based. The .308 Winchester was introduced in 1952, two years prior to the NATO adoption of the 7.62x51mm NATO T65...

, or 5.56 mm

5.56 x 45 mm NATO

5.56×45mm 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 .223

.223 Remington

Manufacturing

Globalization of manufacturing has led to wide adoption of metric standards, although this is not yet universal. After a period where automobile

Automobile

An automobile, autocar, 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 fastener

Fastener

A 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, also driven in part by a shift in manufacturing from the U.S. to countries in Asia with metric standards. Thus, while 5¼-inch floppy disk

Floppy disk

A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...

s had a nominal package size of 5¼ inches (approximately 130 mm), the nominal design diameter of the replacement "3½ inch" disks was actually 90 mm. CD

Compact Disc

The Compact Disc is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage , write-once audio and data storage , rewritable media , Video Compact Discs , Super Video Compact Discs ,...

s and DVD

DVD

A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

s are 120 mm in diameter, but their size is rarely mentioned; Mini CD

Mini CD

Mini CDs, or “pocket CDs” are CDs with a smaller diameter and one third the capacity.-Formats:Amongst the various formats are the* Mini CD single, a small disc. The format is mainly used for audio CD singles in certain regions , much like the old vinyl single...

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 drive 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 display.

Military

The U.S. military uses metric measurements extensively to ensure interoperability with allied forces, particularly NATO STANAG

STANAG

STANAG is the NATO abbreviation for Standardization Agreement, which sets 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...

s, "standardization agreements". Ground forces measure distances in "klicks", slang

Slang

Slang is the use of informal words and expressions that are not considered standard in the speaker's language or dialect but are considered more acceptable when used socially. Slang is often to be found in areas of the lexicon that refer to things considered taboo...

for kilometers. Most military firearms are measured in metric units, beginning with the M-14

M14 rifle

The M14 rifle, formally the United States Rifle, 7.62 mm, M14, is an American selective fire automatic rifle firing 7.62x51mm NATO ammunition. It was the standard issue U.S. rifle from 1959 to 1970. The M14 was used for U.S...

which was introduced in 1957, although a few legacy exceptions exist, such as .50-caliber

Caliber

In guns including firearms, caliber or calibre is the approximate internal diameter of the barrel in relation to the diameter of the projectile used in it....

guns. Aircraft ordnance

Aircraft ordnance

Aircraft ordnance or ordnance is weapons used by aircraft. The term is often used when describing the weight of air-to-ground weaponry that can be carried by an aircraft or the weight that has been dropped...

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 mile

Nautical mile

The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...

s and speed in knots; these units are now accepted for use with SI by the BIPM

International Bureau of Weights and Measures

The International Bureau of Weights and Measures , is an international standards organisation, one of three such organisations 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 cocaine

Cocaine

Cocaine 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, an appetite suppressant, and a topical anesthetic...

) 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-year

Light-year

A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...

in astronomy

Astronomy

Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

). 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 sugar

Blood sugar

The blood sugar concentration or blood glucose level is the amount of glucose present in the blood of a human or animal. Normally in mammals, the body maintains the blood glucose level at a reference range between about 3.6 and 5.8 mM , or 64.8 and 104.4 mg/dL...

levels in milligrams per deciliter, whereas most other countries use millimoles

Mole (unit)

The mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon-12 , the isotope of carbon with atomic weight 12. This corresponds to a value...

per liter. American blood glucose meters have the ability to switch between the two.

Earth sciences, such as hydrology and geology, continue to use customary units for field surveying. This due both to the legacy of many decades of data collection and to the need to work with the construction industry, which has not adopted the metric system. American irrigation engineers, for example, talk in acre-feet and cubic feet per second, whereas their Australian counterparts would refer to gigaliters and cubic meters per second.

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).

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 Games

Olympic Games

The Olympic Games is a major international event featuring summer and winter sports, in which thousands of athletes participate in a variety of competitions. The Olympic Games have come to be regarded as the world’s foremost sports competition where more than 200 nations participate...

.

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. The marathon is referred to as a 26 miles (41.8 km) race (the official marathon standard distance originally being in English units - 26 miles, 385 yards) rather than 42.195 km.

Measured distances as used in events such as shot put

Shot put

The shot put is a track and field event involving "putting" a heavy metal ball—the shot—as far as possible. It is common to use the term "shot put" to refer to both the shot itself and to the putting action....

, high jump

High jump

The 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 certain devices in its modern most practiced format; auxiliary weights and mounds have been used for assistance; rules have changed over the years....

, and discus throw

Discus throw

The discus throw is an event in track and field athletics 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 soccer

Football (soccer)

Association football, more commonly known as football or soccer, is a sport played between two teams of eleven players with a spherical ball...

) were originally set in non-metric units. This is reflected in American football

American football

American football is a sport played between two teams of eleven with the objective of scoring points by advancing the ball into the opposing team's end zone. Known in the United States simply as football, it may also be referred to informally as gridiron football. The ball can be advanced by...

, in which the playing field is divided into yards, and many important statistics are measured in yards. Some sporting equipment, such as ski

Ski

A ski is a long, flat device worn on the foot, usually attached through a boot, designed to help the wearer slide smoothly over snow. Originally intended as an aid to travel in snowy regions, they are now mainly used for recreational and sporting purposes...

s and poles

Ski pole

Ski poles are used by skiers to improve balance and timing. Early ski poles were simply sticks, then bamboo , then steel . In 1958, Ed Scott invented the aluminium ski pole...

, is sold in metric units. The lengths of automobile 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 pool

Swimming pool

A swimming pool, swimming bath, wading pool, or simply a pool, is a container filled with water intended for swimming or water-based recreation. There are many standard sizes; the largest is the Olympic-size swimming pool...

dimensions are 25-yard, 25-meter, and 50-meter. High schools and the NCAA conduct 25-yard competitions. USA Swimming

USA Swimming

USA 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 19

Interstate 19

Interstate 19 is an intrastate Interstate Highway located entirely within the state of Arizona. I-19 runs from Nogales, roughly 1,500 feet from the Mexican border, to Tucson, at Interstate 10...

in Arizona, 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 Route 1, 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.

The 2000 and 2003 editions of the Manual on Uniform Traffic Control Devices

Manual on Uniform Traffic Control Devices

The 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 surface markings, and signals are designed, installed, and used...

were published using both metric and American Customary Units. Metric signs, including speed signs in kilometers per hour, were displayed in the manual even though they were not normally used on the roads and there was no definite plan to go metric. 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. Metric signs and metric measurements were removed for the 2009 edition and replaced with an appendix of metric conversion tables. Officially, this means that, although not widely used, metric road signs are allowed in the United States.
Newer signs on state highways on the island of Kaua‘i

Kauai

Kauai or Kauai, known as Tauai in the ancient Kaua'i dialect, is geologically 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. Known also as the "Garden Isle",...

in Hawai‘i

Hawaii

Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

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.: 5 mi/8 km). In Houston, Texas

Houston, Texas

Houston is the fourth-largest city in the United States, and the largest city in the state of Texas. According to the 2010 U.S. Census, the city had a population of 2.1 million people within an area of . Houston is the seat of Harris County and the economic center of , which is the ...

many speed limits have km/h signs underneath the MPH signs. These are located near both airports and in the Texas Medical Center

Texas Medical Center

The Texas Medical Center is the largest medical center in the world with one of the highest densities of clinical facilities for patient care, basic science, and translational research...

. The U.S. territory of Puerto Rico

Puerto Rico

Puerto Rico , officially the Commonwealth of Puerto Rico , is an unincorporated territory of the United States, located in the northeastern Caribbean, east of the Dominican Republic and west of both the United States Virgin Islands and the British Virgin Islands.Puerto Rico comprises an...

generally uses American-style (MUTCD

Manual on Uniform Traffic Control Devices

) signs with metric measurement on highways, displaying kilometer posts and distances in km, yet speed limit signs are in miles per hour. The Maine Turnpike has metric measurements on its highway signs in addition to Customary measurements, partially to assist the large numbers of Canadian tourists who visit Maine's beaches.

Gasoline and diesel fuel are sold by the U.S. gallon, and fuel economy

Fuel economy in automobiles

Fuel usage in automobiles refers to the fuel efficiency relationship between distance traveled by an automobile and the amount of fuel consumed....

is rated in miles per gallon (MPG). Stations in Point Roberts, Washington

Point Roberts, Washington

Point Roberts is an unincorporated community in Whatcom County, Washington, United States. It has a post office, with the ZIP code of 98281, whose ZIP Code Tabulation Area had a population of 1,314 at the 2010 census.A geopolitical oddity, Point Roberts is a part of the United States that is not...

, a short, discontiguous peninsula that is accessible to the rest of the state of Washington only by crossing into Canada, sells its gasoline from pumps calibrated to dispense in liters. Gasoline is dispensed in liters in Puerto Rico. Automobile crankcase oil is sold by the quart, antifreeze by the gallon, brake fluid by the ounce (fluid), and A/C refrigerant by the ounce (mass). Windshield wiper replacement blades are measured in inches.

Domestic airline flights are assigned altitudes in feet and measure speed in knots. Nautical chart

Nautical chart

A 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 fathom

Fathom

A fathom is a unit of length in the imperial and the U.S. customary systems, used especially for measuring the depth of water.There are 2 yards in an imperial or U.S. fathom...

s and use the nautical mile

Nautical mile

The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...

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 1,852 meters.) Railroads use the standard gauge

Standard gauge

The standard gauge is a widely-used track 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 1,435 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 reported in units derived from both customary and metric units. For example:

Power per unit length of a nuclear reactor fuel rod: kilowatts per foot
Heat rate from a power plant: BTU/kWh
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.
In the Canadian printing industry where ink is sold by the kilogram and paper by the square inch, ink "mileage" is measured in square inches per kilogram or "squinks"
Energy Efficiency Ratio (EER), which is the ratio of an air conditioner's cooling capacity in BTU and its input power in watt-hours. It is used instead of the coefficient of performance, 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. Telephone network lines are measured in kilofeet (KF).

Cultural impact

The continuing use of U.S. customary units has been a cause for speculation in fiction set in the future. Many authors of such works of fiction have assumed that the United States and the human race in general will use metric units in the future; however, some have assumed the continued use of U.S. customary units or have neglected to take metrication into account. 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 Trek
Star Trek: The Original Series
Star Trek is an American science fiction television series created by Gene Roddenberry, produced by Desilu Productions . Star Trek was telecast on NBC from September 8, 1966, through June 3, 1969...

, 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 (TOS episode)

"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 of the show, such as Star Trek: The Next Generation
Star Trek: The Next Generation
Star Trek: The Next Generation is an American science fiction television series created by Gene Roddenberry as part of the Star Trek franchise. Roddenberry, Rick Berman, and Michael Piller served as executive producers at different times throughout the production...

, 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 Simpsons
The Simpsons
The Simpsons is an American animated 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 family of the same name, which consists of Homer, Marge, Bart, Lisa and Maggie...

, Futurama
Futurama
Futurama is an American animated science fiction sitcom created by Matt Groening and developed by Groening and David X. Cohen for the Fox Broadcasting Company. The series follows the adventures of a late 20th-century New York City pizza delivery boy, Philip J...

and The Big Bang Theory
The Big Bang Theory
The Big Bang Theory is an American sitcom created by Chuck Lorre and Bill Prady, both of whom serve as executive producers on the show, along with Steven Molaro. All three also serve as head writers...

. A Saturday Night Live
Saturday Night Live
Saturday Night Live is a live American late-night television sketch comedy and variety show developed by Lorne Michaels and Dick Ebersol. The show premiered on NBC on October 11, 1975, under the original title of NBC's Saturday Night.The show's sketches often parody contemporary American culture...

sketch titled "Decabet," released at the height of the metrication movement, lampooned the different metric measurements by introducing a new alphabet consisting of only ten letters. Popular Science

Popular Science

Popular Science is an American monthly magazine founded in 1872 carrying articles for the general reader on science and technology subjects. Popular Science has won over 58 awards, including the ASME awards for its journalistic excellence in both 2003 and 2004...

's September 2003 edition listed NIST's "Metric System Advocate" on its list of "Worst Jobs in Science".

External links

The United States and the Metric System (LC 1136) nist.gov
The Metric System in the United States
A Metric America: A Decision Whose Time Has Come on nist.gov
Metric Conversion Act of 1975 on nist.gov
US Metric Association (mirror link)
Mean Mr Metric satire about the (non)conversion to metric units. One of the highest scoring submissions to the Internet Oracle
Internet Oracle
The Internet Oracle is an effort at collective humor in a pseudo-Socratic question-and-answer format....

. Originally written by Jim Palfreyman in October 1991.
Waits & Measures
Examples of metric roadsigns in the U.S.
Metrication.us site
Metric 4 US site
Metrication matters site

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