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List of strange units of measurement
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This article describes unusual units of measurement that are sometimes used by anglophone scientists, especially physicists and mathematicians, and other technically-minded people such as engineers and programmers, as bits of dry humor combined with putative practical convenience. See also the list of humorous units of measurement. For units that are primarily used in non-English-speaking countries, please see the article on units specific to that country, links to which can be found in the systems of measurement.
SI units (metre-kilogram-second system) and the imperial system (foot-pound-second system) are the two major systems of measurement.
ng the twentieth century, the Soviets and French briefly used a variant of the metric system where the base unit of mass was the tonne.
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Encyclopedia
This article describes unusual units of measurement that are sometimes used by anglophone scientists, especially physicists and mathematicians, and other technically-minded people such as engineers and programmers, as bits of dry humor combined with putative practical convenience. See also the list of humorous units of measurement. For units that are primarily used in non-English-speaking countries, please see the article on units specific to that country, links to which can be found in the systems of measurement.
Systems of measurement
The SI units (metre-kilogram-second system) and the imperial system (foot-pound-second system) are the two major systems of measurement.
MTS units
During the twentieth century, the Soviets and French briefly used a variant of the metric system where the base unit of mass was the tonne. This meant that a kilogram was a millitonne (mt). Conversely, some companies use the megagram (Mg), to avoid confusion with long or short tons.
FFF units
Most countries use the International System of Units (SI). In contrast, the Furlong/Firkin/Fortnight system of units of measurement draws its attention by being conservative and off-beat at the same time.
One furlong per fortnight is very nearly 1 centimetre per minute (to within 1 part in 400). Indeed, if the inch were defined as 2.54 cm rather than 2.54 cm exactly, it would be 1 cm/min. Besides having the meaning of "any obscure unit", furlongs per fortnight have also served frequently in the classroom as an example on how to reduce a unit's fraction. The speed of light may be expressed as being roughly 1.8 terafurlongs per fortnight.
SI-imperial hybrids
In the U.S., new mongrel units are sometimes formed by a combination of traditional units, still widely used, and metric units. Thus, "grams per fluid ounce" and "grams per pound of bodyweight" are common units used in sports nutrition, for example to express the concentration of carbohydrate in a beverage.
A hybrid standard quantity used in mining is the assay ton (AT), which is as many milligrams as there are Troy ounces in a ton: 29.17 grams if the ton used is the short ton, and 32.67 g if the ton used is the long ton. So to find how many ounces of gold are in a ton of rock, one measures the number of milligrams of gold in an assay ton of rock.
There are also reports of engineers realizing the comfort of base-ten SI prefixes, combining them with Imperial or U.S. customary units instead of making the full switch, for example the kiloyard (914.4 m). The kip or kilopound is regularly used in structural engineering. Similarly, the kilofoot is quite common in U.S. telecommunication engineering, as significant distances in cable route planning are usually given in thousands of feet. Instruments like optical time-domain reflectometers usually have an option to display results in kilofeet. Perhaps most common is the use of the Mil, defined as one thousandth of an inch (25.4 µm), frequently used to measure the thickness of very thin materials like film and plastic sheeting. A related unit is the circular mil, used for measuring the thickness of wire.
In the UK, it is still (2007) not uncommon to find the 'metric-foot' in use in the domestic refurbishment market. A metric foot is 30cm and usually it is used with lumber (timber in the UK) that is only available in metric-yards or 90cm multiples (See metric inch below).
A useful unit when working with optical pathway lengths in the lab is the one foot per nanosecond approximation for the speed of light. In electronic circuitry, where the speed of signal propagation is slightly slower, similar approximations can be used for 'signal races' in the circuitry. (See light nanosecond below.)
Derived units
There are some obscure metric units: with arbitrary units and prefixes, you can express a common unit with an unfamiliar term. Among physicists there is the in-joke replacing common units with uncommon units, as in velocity: metres per second is equivalent to hertz per dioptre (Hz/dpt). In this case, the reciprocal values of metre and second — dioptre and hertz, respectively — are used to contrive the same unit. The becquerel could also be used instead of hertz, as it is a measure of aperiodic events per time, instead of the periodic events per time measured by the hertz.
Length
Mickey
One mickey, named after the cartoon character Mickey Mouse, is defined as the length of the "smallest detectable movement" of a computer mouse. Approximately equal to 0.1 mm, its precise size depends on the equipment used.
Attoparsec
Parsecs are used in astronomy to measure enormous interstellar distances. A parsec is approximately 3.26 light-years or about 3.085×1016 m. Combining it with the "atto-" prefix yields attoparsec (apc), a conveniently human-scaled unit of about 3.085 cm (about 1 7/32 in) that has no obvious practical use.
Interestingly, 1 attoparsec/microfortnight is nearly 1 inch/second (the actual figure is about 1.0043 in/s, or approximately 2.55 cm/s). See mathematical coincidences for a list of similar factoids.
Light-nanosecond
The light-nanosecond was popularized as a unit of distance by Grace Hopper as the distance which a photon could travel in one billionth of a second (roughly 30 cm or one foot): "The speed of light is one foot per nanosecond." In her speaking engagements, she was well-known for passing out light-nanoseconds of wire to the audience, and contrasting it with light-microseconds (a coil of wire 1,000 times as long) and light-picoseconds (the size of ground black pepper). Over the course of her life, she had many motivations for this visual aid: including demonstrating the waste of sub-optimal programming, illustrating advances in computer speed, and simply giving young scientists and policy makers the ability to conceptualize the magnitude of very large and small numbers.
Metric inch
The international inch is defined to be exactly 25.4 mm. It is approximated to 25 mm as a "metric inch".
A metric inch was used in some Soviet computers when Soviet engineers built them based on blueprints drawn in the U.S.. The computers would look like machines made in the U.S., but components were not interchangeable.
The similarly derived metric foot (300 mm) was once used in the United Kingdom for some expensive materials. It was also briefly the unit used in the trade of timber when neither feet nor metres was used.
Storeys (stories)
All buildings are made up of storeys (stories in U.S. English), also referred to as floors or levels. In the United States, each storey is generally 8 to 10 feet (2.4 to 3 metres). The number of storeys is used to express the height of a building or nonbuilding structure.
In Brazil, storeys (andares in Portuguese) are used mainly by the media as a proxy for 3 metres. It's normally employed in situations to express heights of buildings or elevations.
Double-decker bus
In Britain, newspapers and other media will frequently refer to lengths in comparison to the length or height of a London Routemaster double-decker bus. Popular topics for such comparison include the blue whale, the IMAX screen, and the diplodocus.
Football field
The length of an American football field is long. If the end zones are included, it is , but 100 yards is used informally as a unit, to allow easier conversion from formal measurement in feet or yards. It describes the size of a large building or a park, a distance which is not too short, but which one can walk over. Media in the U.K. also uses the football pitch as a unit of length, although an area of a soccer pitch is not fixed, but varies within a limit of in length and in width. The usual size of a football pitch is 105×68 m (115×75 yd), the area used for matches in the UEFA Champions League.
Tall buildings
In the U.S., buildings such as the Empire State Building , Sears Tower , and Seattle Space Needle are used as comparative measurements of height, as are the Statue of Liberty and Washington Monument. The Empire State Building (but not the others mentioned) is also used in Britain for describing particularly large/tall objects.
In the U.K., the Eiffel Tower , Nelson's Column , Blackpool Tower and Big Ben (more correctly "The Clock Tower of the Palace of Westminster") are commonly used by British newspapers or reference books to give the comparative heights of buildings or, occasionally, mountains.
In Canada (and occasionally elsewhere), the Toronto CN Tower , and in the western part of Canada, the Calgary Tower, is used as a unit of length.
Block
A city block (in most U.S. cities) is between 1/16 and 1/8 mi (0.1 and 0.2 km). In Manhattan, the measurement "block" usually refers to a north-south block, which is 1/20 mi (0.08 km). Within a typical large North American city, it is often only possible to travel along east-west and north-south streets, so travel distance between two points is often given in the number of blocks east-west plus the number north-south (known to mathematicians as the Manhattan Metric).
Siriometer
The siriometer is a rarely used astronomical measure equal to one million astronomical units, i.e., one million times the average distance between the Sun and Earth. This distance is equal to about 15.8 light-years, about twice the distance from Earth to the star Sirius.
Circle of the earth
The circumference of a great circle of the earth (about 40,000 km/25,000 mi/21,600 nmi) is often compared to large distances. For example, one might say that a large number of objects laid end-to-end at the equator "would circle the earth four and a half times". According to WGS-84, the circumference of a circle through the poles (twice the length of a meridian) is 40,007,862.917 metres and the length of the equator is 40,075,016.686 m. Despite the fact that the difference (0.17%) between the two is insignificant at the low precision that these quantities are typically given to, it is nevertheless often specified as being at the equator.
Area
Barn
A barn is a unit of area used by nuclear physicists to quantify the scattering cross-section of very small particles, such as atomic nuclei. One barn is equal to 1.0 m².
Outhouse
An outhouse is a unit of area used by nuclear physicists. One outhouse is equal to 1.0 barns. The term was derived by analogy with the barn.
Shed
A shed is a unit of area used by nuclear physicists. One shed is equal to 1.0 barns. The term was derived by analogy with the barn.
Nanoacre
A nanoacre is a unit (about 4 mm²; ˜ 2.01168 mm on a side) of real estate on a VLSI chip. "The term gets its humor from the fact that VLSI nanoacres have costs in the same range as real acres in Silicon Valley once one figures in design and fabrication-setup costs."
Football field
In many countries, a football pitch (association football field) is used as a man-in-the-street unit of area. It is necessarily restricted to order-of-magnitude comparisons by the fact that football pitches are officially allowed to vary by a factor of 2.67 in area (between 4,050 and 10,800 m², i.e., roughly 0.5 to 1 hectare) although this factor drops to 2.01 in the case of pitches approved for international matches. In the UEFA Champions League a football field must be exactly 105x68m, which is an area of 7,140 m². An American Football field, including both end zones, is 360 ft by 160 ft, or 57,600 square-feet (5,351.2 m²).
Various countries, regions, and cities
The area of a familiar country, state or city is often used as a unit of measure, especially in journalism.
In the United Kingdom, Wales, equal to 20,779 km², is used in phrases such as "an area the size of Wales" or "twice the area of Wales". England is 6.5 times the size of Wales, and Scotland is four times the size of Wales. The Isle of Wight (380 km²) is commonly used for smaller areas. The British comedy show The Eleven O'Clock Show parodied the use of this measurement, by introducing a news article about an earthquake in Wales, stating that an area the size of Wales was affected.
In the United States, the areas of Rhode Island (1,545 sq mi/4,002 km², the smallest state and therefore a relatively easy threshold to reach), Texas (268,601 sq mi/742,293 km², commonly used due to its historic "larger than life" reputation), and less commonly used Alaska (656,425 sq mi/1,700,133 km²) are used in a similar fashion. Antarctica's Larsen B ice shelf was approximately the size of Rhode Island until it broke up in 2002. Due to Rhode Island being a relatively small unit of measurement (and, perhaps, due to its area being 33% water), many comparisons to the size of Rhode Island are somewhat imprecise. The U.S. Central Intelligence Agency uses Washington, D.C. as a comparison for city-sized objects.
In Finland, the region of Uusimaa (6,366 km²) is commonly used for area comparisons. In Canada, the standard unit of comparison is often Prince Edward Island, the smallest Canadian province.
In Russia, France is often used as a comparison for regions of Siberia. This was so popular in Soviet time that the phrase "??? ??? ???????" (twice the size of France) became a stock phrase to denote any large area.
Volume
Board foot or super foot
A board foot is an American unit of volume, used for wood. It is equivalent to . However, in practice, it is defined differently for hardwood and softwood. It is also found in the unit of density pounds per board foot. In Australia and New Zealand the terms super foot or superficial foot were formerly used for this unit.
Hoppus Foot
A system of measure for timber in the round (standing or felled), now largely superseded by the metric system except in measuring hardwoods in certain countries. Following the so-called "quarter-girth formula" (the square of one quarter of the circumference in inches multiplied by one 144th of the length in feet), the notional log is four feet in circumference, one inch of which yields the hoppus board foot, 1 foot yields the hoppus foot, and 50 feet yields a hoppus ton. The hoppus board foot, when milled, yields a board foot. The volume yielded by the quarter-girth formula is 78.5% of cubic measure.
Stère
The stère (st) is equal to a cubic metre or kilolitre. The stère is traditionally used to measure a quantity of wood.
In Finnish, the same unit is known as motti (from Swedish mått, "measure").
Olympic-sized swimming pool
For larger volumes of liquid, one measure commonly used in the media in many countries is the Olympic-sized Swimming Pool. A large Olympic swimming pool with dimensions m holds 2.5 million litres, about 2 acre-feet or 1/200,000 of a sydharb.
Sydharb
A unit of volume used in Australia for water. One sydharb (or sydarb), also called a Sydney Harbour, is the amount of water in Sydney Harbour: approximately 500 gigalitres (about 400,000 acre-feet).
Mass
Grave
In 1793, the French term "grave" (from "gravity") was suggested as the base unit of mass for the metric system. In 1795, however, due in no small part to the French Revolution, the name "kilogram" was adopted instead.
Slug
The slug is an English unit of mass. It is a mass that accelerates by 1 ft/s² when a force of one pound-force (lbf) is exerted on it (14.5939 kg).
Bag of Cement
The mass of an old bag of cement was one hundredweight ~ approximately 50 kg. The amount of material that, say, an aircraft could carry into the air is often visualised as the number of bags of cement that it could lift, probably because a single bag of cement is close to the maximum that a person could safely carry. It should be noted that Health and Safety concerns have forced cement manufacturers to sell cement in 25 kg bags in more recent years, possibly negating the usefulness of this unit of measurement.
Time
Shake
In nuclear engineering and astrophysics contexts, the shake (as in "two shakes of a lamb's tail", an old colloquial expression) is used as a conveniently short period of time. 1 shake is defined as 10 nanoseconds.
Jiffy
In computing, the jiffy is the duration of one tick of the system timer interrupt. Typically, this time is 0.01 seconds, though in some earlier systems (such as the Commodore 8-bit machines) the jiffy was defined as 1/60 of a second, roughly equal to the vertical blanking interval on NTSC video hardware (and the frequency of AC electric power in North America).
Microfortnight
One very convenient unit deduced from the FFF system is the millionth part of the fundamental timeunit of FFF, which equals 1.2096 seconds, and is a typical example of computer nerd humour. As the story goes, "The VMS operating system has a lot of tuning parameters that you can set with the SYSGEN utility, and one of these is TIMEPROMPTWAIT, the time the system will wait for an operator to set the correct date and time at boot if it realizes that the current value is bogus. This time is specified in microfortnights".
The joke is in having a rather large unit (fortnight) combined with a fractional SI prefix (micro) to counteract that. The practical purpose is to discourage setting such parameters without some thought. The unit was selected because the time is only approximately one second, being established by some near-infinite loops rather than a real clock unit (which isn't active at the time), and rather than field complaints about this being "not exactly a second", the unit was invented.
Galactic year
The most common large-scale time scale is millions of years (Megaannum or Ma). However, for long-term measurements, this still requires rather large numbers. Using as a measure the time it takes for the solar system to revolve once around the galactic core (GY), approximately 250 Ma, yields some easily memorizable numbers. In this scale, oceans appeared on Earth after 4 GY, life began at 5 GY, and multicellular organisms first appeared at 15 GY. Dinosaurs went extinct about 0.4 GY ago, and the true age of mammals began about 0.2 GY ago. The age of the Earth is estimated at about 20 GY.
Angular Measure
Furman
The Furman is a unit of angular measure equal to of a circle. It is named for Alan T. Furman, the American mathematician who adapted the CORDIC algorithm for 16-bit fixed-point arithmetic sometime around 1980.
A related unit of angular measure equal to of a circle has found some use in machinery control where fine precision is not required, most notably crankshaft and camshaft position in internal combustion engine controllers, but there is no consensus as to its name.
Other SI-compatible scales
Foe: Energy
A foe is a unit of energy equal to 1044 joules that was coined by physicist Gerry Brown of SUNY-Stony Brook. To measure the staggeringly immense amount of energy produced by a supernova, specialists occasionally use the "foe", an acronym derived from the phrase [ten to the power of] fifty-one ergs, or 1051 ergs. This unit of measure is convenient because a supernova typically releases about one foe of observable energy in a very short period of time (which can be measured in seconds).
Langley: Energy intensity
The langley (symbol Ly) is used to measure solar radiation or insolation. It is equal to one thermochemical calorie per square centimetre (4.184 J/m²) and was named after Samuel Pierpont Langley.
Stokes: Kinematic viscosity
One of the few CGS units to see wider use, one stokes (symbol S or St) is a unit of kinematic viscosity, defined as 1 cm²/s, i.e., 10-4 m²/s.
Jansky: Electromagnetic flux
In radio astronomy, the unit of electromagnetic flux is the jansky (symbol Jy), equivalent to 10-26 watts per square metre per hertz (in base units 1 kg/s4). It is named after the pioneering radio astronomer Karl Jansky. The brightest natural radio sources have flux densities of the order of one to one hundred jansky.
Metre of water equivalence
A material-dependent unit used in nuclear and particle physics and engineering to measure the thickness of shielding, for example around a nuclear reactor, particle accelerator, or radiation or particle detector. 1 mwe of a material is the thickness of that material that provides the equivalent shielding of one metre of water.
This unit is commonly used in underground science to express the extent to which the overburden (usually rock) shields an underground space or laboratory from cosmic rays. The actual thickness of overburden through which cosmic rays must traverse to reach the underground space varies as a function of direction due to the shape of the overburden, which may be a mountain, or a flat plain, or something more complex like a cliff side. To express the depth of an underground space in mwe (or kmwe for deep sites) as a single number, the convention is to use the depth beneath a flat overburden at sea level that gives the same overall cosmic ray muon flux in the underground location.
Units for unconventional measurements
Gillette: Laser power
A unit described by Theodore Maiman as an early measure of laser output power. The measure was simply the number of razor blades through which the laser could burn a hole. This measurement was especially convenient as the first lasers were pulsed ruby lasers, making it otherwise difficult to measure the output power. Also, due to the relative uniformity of razor blades manufactured by The Gillette Company, it had some usefulness as a rough comparison.
Thus, scientists would brag about having a "4 Gillette" laser versus their competitor's puny "2 Gillette" laser. (For the record, Ted Maiman claims that the first laser was a "2 Gillette" laser.)
Unit of alcohol: Quantity of alcohol
In the UK, units of alcohol are used in the health industry and some government campaigns to measure the amount of alcohol consumed. One unit is approximately 10 cm³ of ethanol, or about 8 g. The recommended weekly intake is no more than 14 units for women, and 21 units for men.
Sagan: Scalar
A whimsical unit of measure equalling at least 4,000,000,000. Based on the quote "billions of stars" used by Carl Sagan and popularized with the derivation "billions and billions of stars" by Johnny Carson.
Big Mac Index: Purchasing power parity
The Economist's Big Mac Index compares the purchasing power parity of countries in terms of the cost of a Big Mac hamburger. This was felt to be a good measure of the prices of a basket of commodities in the local economy including labour, rent, meat, bread, cardboard, advertising, tomatoes, etc.
A similar system used in the UK is the 'Mars Bar'. Tables of prices in Mars Bars have intermittently appeared in newspapers over the last 20 years, usually to illustrate changes in wages or prices over time without the confusion caused by inflation.
Garn
The Garn is NASA's unit of measure for symptoms resulting from space adaptation syndrome, the response of the human body to weightlessness in space, named after U.S. Senator Jake Garn, who became exceptionally spacesick during an orbital flight in 1985. If an astronaut is completely incapacitated by space adaptation syndrome, he is under the effect of one Garn of symptoms.
KLOC: Computer program length
A computer programming expression, the KLOC, pronounced kay-lok, standing for "kilo-Lines of Code", i.e., thousand lines of code. The unit is used, especially by IBM managers, to express the amount of work required to develop a piece of software. Given that estimates of 20 lines of functional bug-free code per day per programmer were often used, it is apparent that 1 KLOC could take one programmer as long as 50 working days, or 10 working weeks.
Nibble
A measure of quantity of data or information, the "nibble" (sometimes spelled "nybble" or "nybl") is equal to 4 bits, or one half of the common 8-bit byte. The nibble is used to describe the amount of memory used to store a digit of a number stored in packed decimal format, or to represent a single hexadecimal digit.
Nines
Numbers very close to, but below one are often expressed in nines (N - not to be confused with the unit newton), that is in the number of nines following the decimal separator in writing the number in question. For example, "three nines" or "3N" indicates 0.999 or 99.9%, "four nines five" or "4N5" is the expression for the number 0.99995 or 99.995%.
Typical areas of usage are:
- the reliability of computer systems, that is the ratio of uptime to the sum of uptime and downtime. "Five nines" reliability in a continuously operated system means an average downtime of no more than approximately five minutes per year.
- the purity of materials, such as gases and metals.
Proof: Alcohol concentration
Up to the 20th century, alcoholic spirits were assessed in the UK by mixing with gunpowder and testing the mixture to see if it would still burn; spirit that just passed the test was said to be at 100° proof. The UK now uses percentage alcohol by volume at 20 °C, where spirit at 100° proof is approximately 57.15% ABV; the U.S. uses a proof number of twice the ABV at 60 °F (15.5 °C).
Savart: Audible frequency ratio
An 18th century unit for measuring the frequency ratio of two sounds, it is equal to 1/300 of an octave, or 1/25 of a semitone. Still used in some programs, but considered too rough for most purposes. Cent is preferred.
Scoville heat unit: Pepper hotness
The Scoville scale is a measure of the hotness of a chili pepper. It is the degree of dilution in sugar water of a specific chili pepper extract when a panel of 5 tasters can no longer detect its 'heat'. Pure capsaicin (the chemical responsible for the 'heat') has 1.6 Scoville heat units.
ASTA Pungency unit: Pepper hotness
ASTA (American Spice Trade Association) Pungency unit is based on a scientific method of measuring chili pepper 'heat'. The technique utilizes high performance liquid chromatography to identify and measure the concentrations of the various compounds that produce a heat sensation. Scoville units are roughly 15 times higher than Pungency units while measuring capsaicin, so a rough conversion is to multiply Pungency by 15 to obtain Scoville heat units.
Strontium unit: Radiation dose
The strontium unit, formerly known as the Sunshine Unit (symbol S.U.), is a unit of biological contamination by radioactive substances (specifically strontium-90). It is equal to one picocurie of Sr-90 per gram of body calcium. Since about 2% of the human body mass is calcium, and Sr-90 has a half-life of 28.78 years, releasing 6.697+2.282 MeV per disintegration, this works out to about 1.065 grays per second. The permissible body burden was established at 1,000 S.U.
Dol: Pain
The dol (from the Latin word for pain, dolor) is a unit of measurement for pain.
James D. Hardy, Herbert G. Wolff, and Helen Goodell of Cornell University proposed the unit based on their studies of pain during the 1940s-1950s. They defined one dol to equal to "just noticeable differences" (jnd's) in pain. The unit never came into widespread use and other methods are now used to assess the level of pain experienced by patients.
Erlang: Telecommunications traffic volume
The Erlang, named after A. K. Erlang, as a dimensionless unit is used in telephony as a statistical measure of the offered intensity of telecommunications traffic on a group of resources. Traffic of one Erlang refers to a single resource being in continuous use, or two channels being at fifty percent use, and so on, pro rata.
See also
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