For units of measure primarily used in countries where English is not the main language, see the article specific to that country, a list of which can be found in the systems of measurement article.
For unusual units of measure invented primarily for amusement, see List of humorous units of measurement

An unusual unit of measurement is a unit of measurement that does not form part of a coherent system of measurement; especially in that its exact quantity may not be well known or that it may be an inconvenient multiple or fraction of base units in such systems. This definition is deliberately not exact since it might seem to encompass units such as the week or the light-year which are quite "usual" in the sense they are often used; if they are used out of context, they may be "unusual," as demonstrated by the FFF system of units.

Unusual units of measure are sometimes used by scientists, especially physicists and mathematicians, and other technicians, engineers and computer programmers, either humorously or for real convenience when dealing with objects in the real world whose quantities in more conventional units may be awkward to use. Scientists studying nuclear reactions use the barn quite frequently; however, its use is extremely rare for other scientific disciplines. Unusual units are also employed by journalists and science instructors in an attempt to help people who may not be able to grasp extremely large or small numbers or unfamiliar scientific units. "An area the size of Denmark" and the banana equivalent dose are classic examples. Whether such comparisons actually are meaningful is open to debate, since the comparative quantity itself may not be well known with much accuracy. (e.g., what size and cultivar of the banana is the unit based on?)


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.

SI-imperial hybrids

In the US, mongrel units are sometimes formed by a combination of traditional units, which are widely used, and metric units. Thus, "grams per fluid ounce" and "grams per pound of body weight" 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 certain engineers using base-ten SI prefixes in combination with Imperial or US customary units, for example the kiloyard (914.5 m). The kip or kilopound is regularly used in structural engineering. Similarly, the kilofoot is quite common in US telecommunication engineering, as significant distances in cable route planning are usually given in thousands of feet, and such a measurement was used to select the registration number for SpaceShipOne, with its FAA aircraft registration number of N328KF signifying the distance in "kilofeet" from the Earth's surface to the edge of space. Instruments like optical time-domain reflectometers usually have an option to display results in kilofeet. Perhaps most common is the use of the thou or mil, defined as 1/1,000 of an inch (25.4 µm), frequently used in the manufacturing industry and to measure the thickness of very thin materials like film and plastic sheeting. A related unit is the circular mil, used for measuring the cross-sectional area of wire.

In the UK, it is not uncommon to find the "metric foot" in use in the domestic refurbishment market. A metric foot is 30 cm and usually it is used with lumber that is only available in metric yards or 90 cm multiples. Its square form is also common in some fields: for example, carpet and other flooring materials, when supplied in "tiles" (squares), are often supplied in this size. In commercial office fitout in the UK, most suspended ceilings and raised floors are based on a 60 cm module, or 2 "metric feet".

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 velocity of propagation is somewhat slower than the speed of light in a vacuum, similar approximations can be used for "signal races" in the circuitry. (See light-nanosecond below.)

Planck units

Main article: Planck units

Planck units, sometimes called "natural units", were proposed in 1898 by the physicist Max Planck, and are defined by setting certain physical constants to the value equalling to 1. In this system, one metre equals about 6.187×1034 Planck length units, and one second equals 1.854×1043 Planck time units. The speed of light is, by definition, exactly 1 Planck length/Planck time, and many other quantities take on simple forms as well. Because of this, these units are favoured in some branches of physics.



Parsecs are used in astronomy to measure enormous interstellar distances. A parsec is approximately 3.26 light-years or about 3.085×1016 m (1.917×1013 mi). Combining it with the "atto-" prefix yields attoparsec (apc), a conveniently human-scaled unit of about 3.085 centimetres (1.215 in) that is used only humorously.[2]


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."[3] 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 found many uses 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.[4]

Metric foot

A metric foot (defined as 300 mm) has been used occasionally in the UK[5] but has never been an official unit.


Main article: Horse length

Similarly, horses are used to measure distances in horse racing - a horse length (shortened to merely a length when the context makes it obvious) equals roughly 8 feet or 2.4 metres. Shorter distances are measured in fractions of a horse length; also common are measurements of a full or fraction of a head, a neck, or a nose. "Neck and neck" is an example of a Siamese twin which refers to the neck as a unit of measurement in horse racing.


In vehicle driving tests in the UK and elsewhere, braking distances can be given in metres or in car lengths (with a car for this purpose being typically around 4 m long). A "car length" or "length" is also a common unit for estimating the distance between two cars in auto racing.


In Britain, newspapers and other media will frequently refer to lengths in comparison to the length (8.4 metres or 28 feet) or height (4.4 metres or 14 feet) of a London Routemaster double-decker bus.

The UK Department of Transport has changed the definition of the maximum acceptable length dimensions about 40 times since 1900, as suggested by the UK documentary "100 Years of British Buses" (1996).

Similarly, in the United States the yellow school bus is a common point of comparison, with an average length of around 35 feet (11 m) .

Popular topics for such comparison include the blue whale (30 m), the IMAX screen (22 × 16.1 m), and the diplodocus (35 m).[6]

Football field (length)

The length of an American football field is 120 yd (110 m).

The Canadian football field is 65 yards (59 m) wide and 110 yards (100 m) long with end zones 20 yards (18 m) deep.

Media in the UK also use the football pitch as a unit of length, although an area of the association football pitch is not fixed, but varies within a limit of 90–120 m (98–131 yd) in length and 45–90 m (50–100 yd) in width. The usual size of a football pitch is 105 m × 68 m (115 yd × 75 yd), the area used for matches in the UEFA Champions League.

Tall buildings

In the US, buildings such as the Empire State Building (449 m or 1,473 ft), Sears Tower (519 m or 1,703 ft), and Seattle Space Needle (184 m or 604 ft) 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. Before the September 11 attacks, the World Trade Center towers were frequently used in the same fashion.

In France, the Eiffel Tower (324 m or 1,063 ft), and the UK, Nelson's Column (52 m or 171 ft), Blackpool Tower (158 m or 518 ft),[7] Big Ben (officially the Elizabeth Tower: 96.3 m or 316 ft), and St Paul's Cathedral (108 m or 354 ft) 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 (553 m or 1,814 ft) is used as a unit of length.[8][9]


A city block (in most US cities) is between 1/16 and 1/8 mi (100 and 200 m). In Manhattan, the measurement "block" usually refers to a north-south block, which is 1/20 mi (80 m). Sometimes people living in cities with a regularly-spaced street grid will speak of long blocks and short blocks. 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).

The Earth's circumference

The circumference of a great circle of the Earth (about 40,000 km/25,000 mi/21,600 nmi/199,000 furlongs) 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".[10] According to WGS-84, the circumference of a circle through the poles (twice the length of a meridian) is 40,007,862.917 metres (131,259,392.772 ft) and the length of the equator is 40,075,016.686 m (131,479,713.537 ft). 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.

The definitions of both the nautical mile and the kilometre were originally derived from the Earth's circumference as measured through the poles. The nautical mile was defined as a minute of arc of latitude measured along any meridian. A circle has 360 degrees, and each degree is 60 minutes, so the nautical mile was defined as 1/21,600 of the Earth's circumference, or about 1,852.22 metres. However, by international agreement, it is now defined to be exactly 1,852 metres (approximately 6,076 feet).

The kilometre was originally defined as 1/10,000 of the distance from a pole to the equator, or as 1/40,000 of the Earth's circumference as measured through the poles. This definition would make the kilometre's length approximately 1,000.197 metres, whereas it is exactly 1,000 metres (approximately 3,281 feet), of course.

Earth-to-Moon distance

The distance between the Earth's and the Moon's surfaces is, on average, approximately 380,000 km, or 240,000 miles. This distance is sometimes used in the same manner as the circumference of the Earth; that is, one might say that a large number of objects laid end-to-end "would reach all the way to the Moon and back two-and-a-half times."

The abbreviation for the Earth-to-Moon distance is "LD" which stands for "Lunar Distance", used in astronomy to express close approaches of Earth by minor planets.


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, 149.6 Pm or 4.8 parsecs, and is about twice the distance from Earth to the star Sirius.



Main article: Barn (unit)

One barn is 10−28 square metres, about the cross-sectional area of a uranium nucleus. The name probably derives from early neutron-deflection experiments, in which the uranium nucleus was described, comparatively, as being "big as a barn". Additional units include the microbarn (or "outhouse")[11] and the yoctobarn (or "shed").[12][13]


The nanoacre is a unit of real estate on a VLSI chip equal to 0.00627264 sq in (4.0468564224 mm2) or the area of a square of side length 0.0792 in (2.01168 mm). "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."[14]


The square is an Imperial unit of area that is used in the construction industry in North America,[15] and was historically used in Australia by real estate agents. One square is equal to 100 square feet. A roof's area may be calculated in square feet, then converted to squares.

Football field (area)

A football pitch, or field, can be used as a man-in-the-street unit of area.[16][17] The standard FIFA football pitch is 105 m long by 68 m wide (7,140 m2, 0.71 ha, 1.76 acres); FIFA allows for a variance of up to 5 m in length and 4 m in width in either direction (and even larger discretions if the pitch is not used for international competition), which generally results in the association football pitch generally only being used for order of magnitude comparisons.[18]

An American football field, including both end zones, is 360 ft by 160 ft (ca. 110 m × 49 m), or 57,600 square-feet (5,350 m², 0.54 ha, 1.32 acres). A Canadian football field is 65 yards wide and 110 yards long (ca. 101 m × 59 m) with end zones adding a combined 40 yards to the length, making it 87,750 square-feet (8,156 m2, 0.82 ha, 2.01 acres)

An Australian rules football field may be approximately 150 metres (or more) long goal to goal and 135 metres (or more) wide, although the field's elliptical nature reduces its area to a certain extent. A 150 by 135 metre football field has an area of approximately 1.6 ha (3.93 acres, 15,900 m2), twice the area of a Canadian football field and three times that of an American football field.

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.


Equal to 20,779 km2 (8,023 sq mi), the country of Wales is used in phrases such as "an area the size of Wales" or "twice the area of Wales".[19][20] England is 6.275 times the size of Wales, and Scotland is roughly four times the size of Wales. Ireland is four times larger than Wales, and France is about twenty-five times larger.

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. The Radio 4 programme More or Less introduced the idea of "kiloWales" - an area 1000 times the size of Wales. The Register introduced the nanoWales (20.78 m2).

The United States

In the United States the areas of the smallest state, Rhode Island (1,545 sq mi or 4,000 km2), the largest contiguous state, Texas (268,601 sq mi or 695,670 km2), and, less commonly, Alaska (656,425 sq mi or 1,700,130 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. In the 1979 movie The China Syndrome, radiation is expected to contaminate "an area the size of Pennsylvania." Any state may be used in this fashion to describe the area of another country.

The US Central Intelligence Agency uses Washington, D.C. (61.4 sq mi or 159 km2) as a comparison for city-sized objects.

Other countries

In Canada, the standard unit of comparison is often Prince Edward Island (5,683 km2 or 2,194 sq mi),[21] the smallest Canadian province.

In Russia, France (551,695 km2 or 213,011 sq mi) is often used as a comparison for regions of Siberia.[22] This was so popular in the Soviet era that the phrase "как две Франции" (twice the size of France) became a stock phrase to denote any large area.

The country of website dedicated to notable areas which have been compared to that of Belgium.

The Isle of Wight (380 km2 or 147 sq mi), an island off the south coast of mainland England, is commonly used to define smaller areas.

For American audiences, Israel, although shaped dissimilarly, is almost always referred to as roughly the size of New Jersey.[24]

In Germany, the Saarland (2,569.69 km2 or 992.16 sq mi) is often used to define areas.[25]



A pony is 0.75 ounces of liquor, or 34 of a shot.[26]

Metric ounce

A metric ounce is an approximation of the imperial ounce, US dry ounce, or US fluid ounce. These three customary units vary. However, the metric ounce is usually taken as 25 or 30 ml when volume is being measured, or grams when mass is being measured.

The US Food and Drug Administration (FDA) defines the "food labeling ounce" as 30 ml, slightly larger than the 29.6 ml fluid ounce.[27]

The shot glass is a liquid volume measure that varies from country to country and state to state depending on legislation. It is routinely used for measuring strong liquor or spirits when the amount served and consumed is smaller than the more common measures of alcoholic "drink" and "pint". There is a legally defined maximum size of a serving in some jurisdictions. Typical sizes may range from a 25 to 30 ml (0.88 to 1.06 imp fl oz; 0.85 to 1.01 US fl oz) pony shot to a double shot of roughly 90 ml (3.2 imp fl oz; 3.0 US fl oz). In the UK, spirits are sold in shots of 25 ml, approximating the old fluid ounce.

Board foot or super foot

A board foot is a United States and Canadian unit of volume, used for lumber. It is equivalent to 1 inch × 1 foot × 1 foot (144 cu in or 2,360 cm3). 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. Its purpose is to estimate the value of sawn timber in a log, by measuring the unsawn log and allowing for wastage in the mill. Following the so-called "quarter-girth formula" (the square of one quarter of the circumference in inches multiplied by 1144 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.[28] Mathematically, this works out to about 36.05 dm³.

Cord and rick

The cord is a unit of measure of dry volume used in Canada and the United States to measure firewood and pulpwood. A cord is the amount of wood that, when "ranked and well stowed" (arranged so pieces are aligned, parallel, touching and compact), occupies a volume of 128 cubic feet (3.62 m3).[29] This corresponds to a well stacked woodpile 4 feet deep by 4 feet high by 8 feet wide (122 cm × 122 cm × 244 cm), or any other arrangement of linear measurements that yields the same volume. An even more unusual measurement for firewood is the "rick". It is stacked 16 inches (40.6 cm) deep with the other measurements kept the same as a cord, making it 13 of a cord; however, regional variations mean that its precise definition is nonstandardized.[30]

Twenty-foot equivalent unit

The twenty-foot equivalent unit is the volume of the average shipping container or railroad boxcar. It is occasionally called a boatload, carload, or shipload. It is equivalent to 1,360 ft3 (39 m3).


Main article: Acre-foot

An acre-foot is a unit of volume commonly used in the United States in reference to large-scale water resources, such as reservoirs, aqueducts, canals, sewer flow capacity, and river flows. It is defined by the volume of one acre of surface area to a depth of one foot, which is ca. 1233.5 m3.

Olympic-size swimming pool

For larger volumes of liquid, one measure commonly used in the media in many countries is the Olympic-size swimming pool.[31] An Olympic swimming pool with dimensions 50 m × 25 m × 2 m (approx 164 ft × 82 ft × 6.6 ft) holds 2,500 m3 (about 2 acre-feet, 550,000 imp gal or 660,000 US gal).


A buddy (Bd) is a volume equal to 1.538 microliters, usually as applied to soft drinks. The term originates from the American convenience store Kwik Trip beverage size, the Mega Buddy, which holds 52 fluid ounces.

Royal Albert Hall

The Royal Albert Hall, a large concert hall, is sometimes used as unit of volume in the UK, particularly when referring to volumes of rubbish placed in landfill.[32] The volume of the auditorium is between 3 and 3.5 million cubic feet (between 85,000 and 99,000 cubic metres).[33]

Sydney Harbour

A unit of volume used in Australia for water. One Sydney Harbour, also called a Sydharb (or sydarb), is the amount of water in Sydney Harbour: approximately 500 gigalitres (400 thousand acre-feet).[34]



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.[35]

Bag of cement and bag mix

The mass of an old bag of cement was one hundredweight ~ 112 lb, 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. In the concrete and petroleum industry, however, a bag of cement is defined as 94 pounds (~ 42.6 kg), because it has an apparent volume close to 1 cubic foot.[36] When ready-mix concrete is specified, a "bag mix" unit is used as if the batching company mixes 5 literal bags of cement per cubic yard (or cubic metre) when a "5 bag mix" is ordered.

Fully loaded 747

The maximum takeoff weight of most earlier models of the Boeing 747 is 800,000 pounds, or 360 tonnes. In the media, multiples of this mass can be used to describe very heavy objects, especially freight trains, e.g. "It weighs as much as five fully loaded 747s."


When reporting on the masses of extrasolar planets, astronomers often discuss them in terms of multiples of Jupiter's mass (1.9 ×1027 kg).[37] For example, "Astronomers recently discovered a planet outside our Solar System with a mass of approximately 3 Jupiters." Furthermore, the mass of Jupiter is nearly equal to one thousandth of the mass of the Sun.


Solar mass (M = 2.0×1030 kg) is also often used in astronomy when talking about masses of stars or galaxies, for example the Milky Way has a mass of approximately 6 ×1011 M.

Solar mass also has a special use when estimating orbital periods and distances of 2 bodies using Kepler's laws: a3 = MtotalT2, where a is length of semi-major axis in AU, T is orbital period in years and Mtotal is the combined mass of objects in M. In case of planet orbiting a star, Mtotal can be approximated to mean the mass of the central object. More specifically in the case of Sun and Earth the numbers reduce to Mtotal ~ 1, a ~ 1 and T ~ 1.



Isaac Asimov proposed in one of his essays that it would be useful to measure time by the linear interval needed by light to travel it. Thus, a "light-foot" would be the time (approximately 1 nanosecond) for light to travel 1 foot (30.48 cm) in a vacuum. Similarly, "light-mile", "light-centimetre". The construction is the inverse of "light-year", which names a time unit in order to measure distance.


In nuclear engineering and astrophysics contexts, the shake is sometimes used as a conveniently short period of time. 1 shake is defined as 10 nanoseconds.[38]


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 refresh period (i.e. the field rate) on NTSC video hardware (and the period of AC electric power in North America).


One unit derived from the FFF system of units is the microfortnight, one millionth of the fundamental time unit of FFF, which equals 1.2096 seconds. This is a fairly representative example of "hacker humor",[39] and is occasionally used in operating systems; for example, the OpenVMS TIMEPROMPTWAIT parameter is measured in microfortnights.[40]


A unit sometimes used in computing. The term is believed to have been coined by IBM in 1969 from the design objective "never to let the user wait more than a few nanocenturies for a response".[41] A nanocentury is approximately 3.155 seconds although Tom Duff is frequently cited as saying that, to within half a percent, a nanocentury is pi seconds.[42]


A moment is a medieval unit of time equal to 90 seconds[43] and a Hebrew calendar measurement equal to 5/114 of a second, or just under 0.044 seconds.[44]

Decimal time systems

Main article: Decimal time

The measurement of time is unique in SI in that while the second is the base unit, and measurements of time smaller than a second use prefixed units smaller than a second (e.g. microsecond, nanosecond, etc.), measurements larger than a second instead use traditional divisions, including the sexagesimal-based minute and hour as well as the less regular day and year units. SI allows for the use of larger prefixed units based on the second, a system known as metric time, but this is unusual.

There have been numerous proposals and usage of decimal time, most of which were based on the day as the base unit. For instance, in dynastic China, the was a unit that represented 1/100 of a day. (It has since been refined to 1/96 of a day, or 15 minutes.) In France, a decimal time system in place from 1793 to 1805 divided the day into 10 hours, each divided into 100 minutes, in turn each divided into 100 seconds; the French Republican Calendar further extended this by assembling days into ten-day "weeks." Ordinal dates and Julian dates allow for the expression of a decimal portion of the day.[45] In the mid-1960s, to defeat the advantage of the recently introduced computers for the then popular rally racing in the Midwest, competition lag times a few events were given in centids (1/100 day, 864 seconds, 14.4 minutes), millids (1/1000 day, 86.4 seconds) and centims (1/100 minute, 0.6 seconds) the latter two looking and sounding a bit like the related units of minutes and seconds. Decimal time proposals are frequently used in fiction, often in futuristic works.

In addition to decimal time, there also exist binary clocks and hexadecimal time.

Dog year

A unit of measurement equal to one seventh of a year, or approximately 52 days, is primarily used to approximate the equivalent age of dogs and other animals with similar life spans. It is based upon a popular myth regarding the aging of dogs that states that a dog ages seven years in the time it takes a human to age one year. (In fact, the aging of a dog varies by breed; dogs also develop faster and have longer adulthoods relative to their total life span than humans. Most dogs are sexually mature by 1 year old, which corresponds to perhaps 13 years old in humans.[46]) While the typical convention is to identify the "dog year" as the shorter length of time than the standard "human year" (thus, a 12-year-old dog is said to be 84 "in dog years"),[47] it is also not unheard of to have the 52-day unit be identified as a "human year" and the full 365-day year as a "dog year". When the unit is used, measurements in both "dog years" and "human years" are generally included together, to more clearly indicate which name is used for each unit.

Galactic year

Main article: 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 - not to be confused with Gyr for gigayear), 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 1/4 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.[48]

Angular measure


The Furman is a unit of angular measure equal to 165,536 of a circle, or just under 20 arcseconds. It is named for Alan T. Furman, the American mathematician who adapted the CORDIC algorithm for 16-bit fixed-point arithmetic sometime around 1980.[49] 16 bits give a resolution of 216 = 65536 distinct angles. A related unit of angular measure equal to 1256 of a circle has found some use in controllers for high-speed machinery where fine precision is not required, most notably crankshaft and camshaft position sensing in internal combustion engine controllers. It has been called the 8-Bit Furman, the Small Furman, the Furboy and more recently, the miFurman, (milli-binary-Furman) but there is not yet a consensus as to its name.

Binary degree, binary radian, brad

A related unit of angular measure equal to 1256 of a circle, represented by 8 bits, 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. This unit is also used in video game programming. These units are convenient because they form cycles: for the 8-bit unit, the value overflows from 255 to 0 when a full circle has been traversed. Measures are often made using a Gray code, which is trivially converted into more conventional notation.

Angular mil

The angular mil is used by many military organisations to measure plane angle and so to triangulate distances, given an object's apparent and actual size. It is approximately the angle which has a tangent of 1/1000; in NATO standard, this is rounded to 1⁄6400 of a circle, although other definitions are in use. Its name derives from Latin: millesimus ("thousandth") and so the fact it is used mostly by the military is coincidental to its name.[50]


Gallon gasoline equivalent

In 2011 the United States Environmental Protection Agency introduced the gallon gasoline equivalent as a unit of energy because their research showed most US citizens do not understand the standard units. The gallon gasoline equivalent is defined as 33.7 kWh.[51]

Tons of TNT equivalent

The explosive energy of various amounts of the explosive TNT (kiloton, megaton, gigaton) is often used as a unit of explosion energy, and sometimes of asteroid impacts and violent explosive volcanic eruptions. One ton of TNT is 4.184 × 109 joules, or 109 thermochemical calories (≈3.964 × 106 BTU). This definition is not based on the actual physical properties of TNT.

Hiroshima bomb and Halifax explosion

The energy released by the Hiroshima bomb explosion (about 15 kt TNT equivalent, or 6 × 1013 J) is often used by geologists as a unit when describing the energy of earthquakes, volcanic eruptions and asteroid impacts.

Prior to the detonation of the Hiroshima bomb, the size of the Halifax Explosion (about 3 kt TNT equivalent, or 1.26 × 1013 J), was the standard for this type of relative measurement. Each explosion had been the largest known man-made detonation to date.[52]


A foe is a unit of energy equal to 1044 joules (≈9.478 × 1040 BTU) that was coined by physicist Gerry Brown of Stony Brook University. 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).

Other metric-compatible scales

Flow: Amazon River

The volume of discharge of the Amazon River sometimes used to describe large volumes of water flow such as ocean currents. The unit is equivalent to 216,000 m3/s.[53]


Main article: Electronvolt § Mass

It is common in particle physics, where mass and energy are often interchanged, to use eV/c2, where c is the speed of light in a vacuum (from E = mc2). Even more common is to use a system of natural units with c set to 1, and simply use eV as a unit of mass.

1 amu = 931.46 MeV/c2

Energy intensity

The langley (symbol Ly) is used to measure solar radiation or insolation. It is equal to one thermochemical calorie per square centimetre (4.184×104 J/m2 or ≈3.684 BTU/sq ft) and was named after Samuel Pierpont Langley.

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 (≈1.08×10−3 sq ft/s).

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 (= 10−26 kg/s2 in base units, about 8.8×10−31 BTU/ft2). 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 (≈39.4 in) 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.

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 1.065×10 grays per second. The permissible body burden was established at 1,000 S.U.

Banana equivalent dose

Bananas, like most organic material, naturally contain a certain amount of radioactive isotopes—even in the absence of any artificial pollution or contamination. The banana equivalent dose, defined as the additional dose a person will absorb from eating one banana, expresses the severity of exposure to radiation, such as resulting from nuclear weapons or medical procedures, in terms that would make sense to most people. This is approximately 78 nanosieverts - in informal publications one often sees this estimate rounded up to 0.1 μSv.


Data volume

Volume or capacity of data are often compared to various famous works of literature or to large collections of writing. Popular units include Bibles, Encyclopaediae, the complete works of Shakespeare, and the Library of Congress.

When the Compact Disc began to be used as a data storage device, the CD-ROM, journalists had to compare the disc capacity (650 megabytes) to something everyone could imagine. Since many Western households had a Christian Bible, and the Bible is a comparatively long book, it was often chosen for this purpose. The King James Version of the Bible in uncompressed plain 8-bit text contains about 4.5 million characters,[54] so a CD-ROM can store about 150 Bibles.

The print version of the Encyclopædia Britannica is another common data volume metric. It contains approximately 300 million characters,[55] so two copies would fit onto a CD-ROM and still have 50 megabytes (or about 11 bibles) left over.

The term Library of Congress is often used as an unusual unit of measurement to represent an impressively large quantity of data when discussing digital storage or networking technologies. It refers to the US Library of Congress. Information researchers have estimated that the entire print collections of the Library of Congress represent roughly 10 terabytes of uncompressed textual data.[56]

Diagrams and photographs are not included in the total. Since these take up considerably more space than text, this would be an important consideration for digital storage of large book collections. In practice, diagrams can often be expressed more compactly using vector graphics, and data compression software can pack more text into the available space. English text can be compressed to about 11% of its original size.[57] Thus, one might claim that the entire print collections of the Library of Congress could be packed onto a single 2.2 terabyte storage unit, so long as one excluded images, ignored foreign language holdings, and did not count the growth of the print collections by at least 6 million volumes since the time of the study that produced the 10 terabyte number.[58][59] Furthermore, the modern Encyclopædia Britannica contains over 35000 image, audio, and video assets and fits on a single DVD-ROM.[60]

Though some sources have suggested that 10 terabytes represents the total quantity of data stored at the Library of Congress,[61][62][63][64][65][66][67][68][69] this is a significant underestimate, given that the Web Archiving program[70] had by itself collected 385 terabytes of data as of January 2013.[71] A slide from a September 2012 presentation by a Library of Congress storage engineer furthermore noted institutional storage capacity in excess of 27 petabytes,[72] casting further doubt on the accuracy of the 10 terabyte number as applied to the entire holdings.

The Library of Congress itself has made no official claims of how much data is represented by its entire holdings, and several employees have expressly disavowed any of the specific numbers that have been attributed.[73][74]

A similar unit of measure for early computers was phone numbers and phone books.

Big Mac Index: purchasing power parity

Main article: Big Mac Index

The Economist's Big Mac Index compares the purchasing power parity of countries in terms of the cost of a Big Mac hamburger.[75] 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, lettuce, 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.[76]


Chess software frequently uses centipawns internally or externally as a unit measuring how strong each player's situation position is, and hence also by how much one player is beating the other, and how strong a possible move is. 100 centipawns = the value of 1 pawn - more specifically, something like the average value of the pawns at the start of the game, as the actual value of pawns depends on their position. Loss of a pawn will therefore typically lose that player 100 centipawns (which is usually enough to lose the game). The centipawn is a convenient size for choosing between different possible moves, as in a given position, chess software will often rate the better of two moves within a few centipawns of each other.


Main article: FLOPS

In computing, FLOPS (FLoating point Operations Per Second) is a measure of a computer's computing power. It is also common to see measurements of kilo-, mega-, and teraFLOPS.

It is also used to compare the performance of algorithms in practice.


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 US Senator Jake Garn, who became exceptionally spacesick during an orbital flight in 1985. If an astronaut is completely incapacitated by space adaptation syndrome, he or she is under the effect of one Garn of symptoms.[77]

KLOC: computer program length

A computer programming expression, the K-LOC or KLOC, pronounced kay-lok, standing for "kilo-Lines of Code", i.e., thousand lines of code. The unit was used, especially by IBM managers,[78] to express the amount of work required to develop a piece of software. Given that estimates of 20 lines of functional code per day per programmer were often used, it is apparent that 1 K-LOC could take one programmer as long as 50 working days, or 10 working weeks. This measure is no longer in widespread use because different computer languages require different number of lines to achieve the same result.

Error rates in programming are also measured in "Errors per K-LOC", which is called the defect density. NASA's SATC is one of the few organisations to claim zero defects in a large (>500K-LOC) project, for the space shuttle software.

A rare multiple of K-LOC is GLOC, pronounced jee-lok, standing for "giga-lines of code".


Main article: Micromort

A micromort is a unit of risk measuring a one-in-a-million probability of death (from micro- and mortality). Micromorts can be used to measure riskiness of various day-to-day activities. A microprobability is a one-in-a million chance of some event; thus a micromort is the microprobability of death. For example, smoking 1.4 cigarettes increases one's death risk by one micromort, as does traveling 230 miles by car.

Mother Cow Index

Formerly used in real estate transactions in the American Southwest, it was the number of pregnant cows an acre of a given plot of land could support. It acted as a proxy for the agricultural quality, natural resource availability, and arability of a parcel of land.[79]


A measure of quantity of data or information, the "nibble" (sometimes spelled "nybble" or "nybl") is normally 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 binary-coded decimal format, or to represent a single hexadecimal digit. Less commonly, 'nibble' may be used for any contiguous portion of a byte of specified length, e.g. "6-bit nibble"; this usage is most likely to be encountered in connection with a hardware architecture in which the word length is not a multiple of 8, such as older 36-bit minicomputers.


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. (See high availability for a chart.)
  • The purity of materials, such as gases and metals.


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.

Pepper Heat

ASTA pungency unit

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.[80]

Scoville heat unit

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'.[81] Pure capsaicin (the chemical responsible for the 'heat') has 1.6×107 Scoville heat units.[82]

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 (68 °F), where spirit at 100° proof is approximately 57.15% ABV; the US uses a "proof number" of twice the ABV at 60 °F (15.5 °C).


The Savart is 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.

Schmidt sting pain index and Starr sting pain index

These are pain scales rating the relative pain caused by different hymenopteran stings. Schmidt has refined his Schmidt Sting Pain Index (scaled from 1 to 4) with extensive anecdotal experience, culminating in a paper published in 1990 which classifies the stings of 78 species and 41 genera of Hymenoptera. The Starr sting pain scale uses the same 1-to-4 scaling. In practice, the Comparative Pain Scale is used by doctors when working with patients.[83]

Stadium capacities

The number of people that met a condition is often measured with the capacity of major sports and arts facilities, usually the largest ones in a region. For example, Uruguay's Estadio Centenario is often used in Uruguay,[84][85] while in parts of the United States, Michigan Stadium is used in this manner.

Telecommunications traffic volume

Main article: Erlang (unit)

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. A lot of telecommunications management and forecasting software uses this unit on a day to day basis—but strictly speaking it is a telecom sector specific network stress measurement unit.

X-ray intensity

Main article: Crab (unit)

The crab is defined as the intensity of X-rays emitted from the Crab Nebula at a given photon energy up to 30 kiloelectronvolts. The Crab Nebula is often used for calibration of X-ray telescopes. For measuring the X-ray intensity of a less energetic source, the milliCrab (mCrab) may be used.

See also


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