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 HowMany - Unit Dictionar
Category: Mathematics and statistics > Dictionary of unit measurements
Date & country: 26/09/2008, USA
Words: 1293


aas
see 'as' below.

absorbance unit (AU)
a logarithmic unit used to measure optical density, the absorbance of light transmitted through a partially absorbing substance. If T is the percentage of light transmitted, then the absorbance is defined to be -log10 T absorbance units. An increase in absorbance of 1.0 AU corresponds to a reduction in transmittance by a fact...

abv, abw
symbols for alcohol by volume and alcohol by weight. 1% abv = 1% v/v and 1% abw = 1% w/v.

academic year
a unit of time in U.S. schools, generally equal to 9 months.

acfm
abbreviation for 'actual cubic feet per minute.' See under sccm.

acre inch (ac in)
a unit of volume equal (of course) to 1/12 acre foot. An acre inch contains exactly 3630 cubic feet, about 27 154.29 U.S. gallons, or about 102.7902 cubic meters.

AD
abbreviation for the Latin anno domini, 'year of the Lord,' the traditional designation for years of the common or Christian era. This abbreviation is often replaced by CE (common era), especially in countries where Christianity is not a dominant religion.

Admiralty mile
see nautical mile.

agate, agate line
a traditional unit of distance used in printing and advertising. The agate line is equal to 1/14 inch (1.814 millimeters). Its name comes from the traditional type size called agate, which sets approximately 14 lines to the inch (very small print!).

AH
abbreviation for the Latin anno hegirae, traditionally used in the West to designate years of the Islamic calendar. The Islamic calendar is lunar, counting twelve lunar months to the year (see month ). Thus its years are shorter than ordinary solar years. Years are counted from the day of the Hijri (Hegira in Latin), the flight of Mohamm...

air mass
a unit used in astronomy in measuring the absorption of light from the stars by the atmosphere. One air mass is the amount of absorption of light from a star directly overhead (at the zenith). The absorption of light from other stars is greater, because their light must pass obliquely through the atmosphere. If Z is the zenithal angle, the angle be...

air watt
an engineering unit used to express the effective cleaning power of a vacuum cleaner or central vacuum system. The air watt is practically the same as the ordinary watt. Measurements of vacuum power, however, are computed from English units using the following formula established by the American Society for Testing and Materials (ASTM): power in ai...

ale gallon
a traditional unit of liquid volume in Britain and the U.S., the ale gallon was equal to 282 cubic inches (4.6212 liters) or about 1.2208 U.S.liquid gallon (1.0165 British imperial gallon). Standardized in the sixteenth century under Queen Elizabeth I, the ale gallon remained in use well into the nineteenth century but is obsolete today. It is also...

alpha TE
an abbreviation for 'alpha tocopherol equivalent,' a measure of vitamin E used in nutrition. Vitamin E is actually a group of related chemical compounds called tocopherols. The activity, or potency, of vitamin E in a food or food supplement is measured by the quantity (in milligrams) of alpha tocopherol (the most active of the forms of the vitamin)...

alt h
traditional abbreviation in pharmacy for alternis horis, every other hour, a unit of frequency sometimes used in medical prescriptions.

AM or am
abbreviation for the Latin ante meridiem, 'before noon,' used after a time to indicate that the time is before 12:00 (noon). The notations 'AM' and 'PM' are used extensively in the United States, where time is usually not stated on a 24-hour basis. Note: the ambiguous notation '12:00 am' should not be used, since it may be taken to mean either noon...

AM
abbreviation for the Latin anno mundi, 'year of the world.' This abbreviation is traditionally used to designate years in the Jewish calendar, which counts years from the creation of the world as described in the Hebrew scriptures. The Jewish calendar is lunisolar; its years correspond to ordinary solar years (see month ). The first day ...

amagat
units used by physicists to express the relative volume and density of gases. The amagat volume unit is about 22.414 liters per mole (L/mol) or 0.022 414 m3/mol, the volume occupied by a gas at standard temperature (0.01°C) and standard pressure (1 atmosphere). The amagat density unit represents the corresponding relativ...

amber
an old English unit of volume, used for both liquids and dry goods. The amber was equal to about 4 bushels or roughly 140 liters.

American run
see run.

anchor
another name for the anker (see below).

angular mil
see mil .

animal unit (AU)
a unit of feed consumption used in U.S. dairying and ranching. One animal unit is the feed or grazing requirement of a mature cow weighing 1000 pounds (453.59 kilograms). This is approximately 26 pounds (11.8 kg) of dry forage. Total feed requirements are often figured by the animal unit month (AUM), the feed required to sustain one animal unit of ...

anker or anchor
a small wine barrel used in Britain and elsewhere in northern Europe. In England an anker usually held 10 wine (U.S. liquid) gallons (37.85 liters); the Scottish anker held 20 Scots pints (about 34 liters). The word anker is of Dutch origin.

annual percentage rate (% APR)
a unit used in the U.S. for stating interest rates and rates of return on investment. By federal regulation, these rates can be stated however a financial institution wishes, but they must be stated also in % APR so that consumers can compare rates of different loans and investment opportunities. Mathematically, the natural rate r of return on mone...

Apgar score
a numerical measure of the health of a newborn baby. One minute after birth (and at regular intervals thereafter through the first moments of life) newborns are rated 0, 1, or 2 on five indicators of health (respiratory effort, heart rate, skin color, muscle tone, and reflexive response to smell). Possible scores therefore range from 0 to 10. The u...

API degree, API gravity
see degree API.

apothecary weights
a version of the troy weight system formerly used by apothecaries (pharmacists). The troy pound, equal to 373.242 grams or 13.165 72 avoirdupois ounces, is always divided into 12 ounces, each ounce being equal to 480 grains. In the apothecary system, the ounce is divided into 8 drams (60 grains) each containing 3 scruples (20 grains). There is a pa...

arm's-length
in English the term 'arm's-length' is used figuratively to mean 'a distance discouraging familiarity or conflict.' In many cultures, however, the length of a human arm is standardized as a unit of distance equal to about 70 centimeters or 28 inches. Examples include the Italian braccio, the Russian sadzhen, and the Turkish pik.

arpent
a traditional unit of area in French North America (Québec and Louisiana), equal to one square arpent . The arpent of area equals 900 square toises, 100 (square) perches, approximately 0.8445 acre or 0.3419 hectare. By the official Canadian definition, the arpent of area contains 36 800.667 23 English square feet or about 0.844 82...

arratel or artel
versions of a traditional Arab unit of weight; see rotl. The spelling 'arratel' is used in Portugal as an alternate name for the libra.

as
a symbol used in astronomy for the arcsecond (see above).

as, ass, or aas
a traditional unit of mass for gold and silver, used in most of northern Europe but not in England. The unit varied in size from about 48 to 58 milligrams (0.75 to 0.90 English grain).

at
symbol for the technical atmosphere.

atomic number
The atomic number was originally defined (about 1865) simply as an index describing the position of an element in the periodic table. Not until 1913 was it known that the atomic number is actually a unit of measurement, equal to the number of electrons surrounding a neutral (uncharged) atom, and also to the number of protons in the nucleus.

aume
an old English wine measure equal to about 40 gallons (roughly 150 liters). The aume is the English version of a German unit, the ohm .

aune
a traditional French unit of distance, varying from region to region but similar in length to the English ell.

av or avdp
abbreviations for avoirdupois (see below).

AWG
abbreviation for American Wire Gauge. See gauge and the table of wire gauge equivalents.

bag
another name for a sack (3 bushels) used as unit of measure in Britain.

bag
an old English unit of weight, varying with the contents of the bag but generally in the range of 2-4 hundredweight (100-200 kilograms).

bag
a unit of weight for cement. Traditionally a bag of portland cement weighs 94 pounds (42.6 kilograms) in the US. and 87.5 pounds (39.7 kilograms) in Canada. However, cement is now being sold also in metric-sized bags of 50 kilograms (110.2 pounds) by many suppliers.

baht
a traditional weight unit in Thailand, now equal to exactly 15 grams or 1/40 catty (0.5291 ounce). The baht, originally the weight of a silver coin of the same name, is used to measure the weight of precious metals. The unit is pronounced bot.

Balling
a unit of density; see degree Plato.

balthazar
a large wine bottle holding about 12 liters, 16 times the volume of a regular bottle.

bank cubic meter (BCM)
a traditional unit of volume in coal mining. A bank cubic meter represents the contents of a cubic meter of rock in place, before it is drilled and blasted.

bar abs, bar dif
symbols indicating pressures measured in bars. bar abs indicates bars absolute, measuring the total pressure including the pressure of the atmosphere. bar dif indicates bars differential, measuring a difference between two pressures, neither of which is atmospheric pressure.

barg
symbol for bar gauge, a common unit of pressure in engineering. The term 'gauge' means that the pressure has been read from a gauge that actually measures the difference between the pressure of the fluid or gas and the pressure of the atmosphere.

barge
an informal unit of volume used in the U.S. energy industry. The barges used on American rivers customarily carry about 25 000 barrels of oil (see barrel below). This is equivalent to 1.05 million gallons, roughly 1400 register tons, or about 3975 cubic meters.

barrel (bbl)
a commercial unit of weight, varying with the commodity being measured. In the U.S., for example, a barrel of flour traditionally holds 196 pounds (88.90 kg) and a barrel of beef, fish, or pork 200 pounds (90.72 kg). A barrel of cement is traditionally equal to 4 bags, which is 376 pounds (170.55 kg) in the U.S. and 350 pounds (158.76 kg) in Canada...

barrel bulk
a commercial unit of volume equal to exactly 5 cubic feet or 0.141 584 cubic meters. There are exactly 8 barrels bulk in a freight ton and 20 in a register ton.

barrer or Barrer
a CGS unit of gas permeability for membranes, contact lenses, and similar thin materials. Permeability is defined to be the gas flow rate multiplied by the thickness of the material, divided by the area and by the pressure difference across the material. To measure this quantity, the barrer is the permeability represented by a flow rate of 10
barrique
a large French wine barrel holding 225 liters (about 59.44 U.S. gallons).

basis weight
a unit used in the paper industry to express the weight (really, the thickness) of paper. The basis weight is the weight in pounds of one ream (500 sheets) of a basic size sheet. For details, see pound weight.

Baumé
a measure of relative density; see degree Baumé.

BC, BCE
abbreviations for 'before Christ' and 'before common era,' respectively. These are standard designations for years before the beginning of the common or Christian era (see CE). Oddly, there is no year designated 0 in the common system for numbering years; the year 1 CE (or 1 AD) was preceded by 1 BCE (or 1 BC). The lack of a year 0 means that the n...

Bcfe
a symbol used in the natural gas industry for 1 billion cubic feet of gas equivalent (cfe). This is really an energy unit equal to about 1.091 petajoules (PJ).

bcm
abbreviation for 'bank cubic meter' (see above).

bead sizes
see aught.

beer gallon, beer and ale gallon
see ale gallon.

bee space
an informal unit of distance used in beekeeping. In a hive, bees seal up an opening smaller than a bee space, and they fill a larger opening with new honeycomb. If an opening is equal to a bee space, the bees leave it open as a passageway. A hive can be disassembled to remove the honey if the individual comb frames are carefully spaced one bee spac...

BeV
a symbol sometimes used in the U.S. for one billion (109) electronvolts. The correct symbol is GeV.

bhp
abbreviation for brake horsepower. The brake horsepower of an engine is the effective power output, sometimes measured as the resistance the engine provides to a brake attached to the output shaft. See horsepower.

biannually
a confusing expression of frequency. The word is used both for twice a year and for once every two years, so it should be avoided. Twice a year is semiannually and once every two years is biennially.

bicron (µµ)
an obsolete metric unit of distance, defined as 10-12 meter or 10-6 micron. This distance is now called a picometer (pm). The name is a reference to the double prefix in 'micromicron.'

billennia
a new word meaning 'billions of years,' billennia is appearing informally in science writing in phrases such as 'countless billennia' or 'the billennia of evolutionary time.' The word billennium was coined for another purpose, however; it is a registered trademark of the Billennium® Organizing Committee and is used, in the words of a committee ...

billet
a single stick of firewood. Traditional English billets had a length of 40 inches (1.016 meters).

billiard
a unit of quantity equal to 1015, which is one quadrillion in American terminology or 1000 billion in traditional British terminology. The name is coined to parallel milliard, which has long been a name for 1000 million.

billion (bn or B)
a number equal to 1000 million in the U.S. but one million million in traditional British usage. See Names for Large Numbers for a discussion of the billion problem. The symbol bn is often used for billion, especially in Britain; Americans also use B.

bimester
a rarely-seen unit of time equal to 2 months.

bimillennium
a unit of time equal to 2000 years.

bind
an old English unit of quantity for eels, equal to 250.

bips
informal name for the bit per second (see below).

bit (b)
a unit of information content, now known also as the shannon. In information and communications theory, if a message has probability p of being received, then its information content is -log2 p shannons. This unit is often called the bit, because if the message is a bit string and all strings are equally likely to be received...

blink
a unit of time equal to 10-5 day or exactly 0.864 second. This unit is also called the metric second; in most metric time proposals, the day is divided into 10 hours, each hour into 100 minutes (called beats in 'Internet time': see 'beat' above), and each minute into 100 seconds or blinks. An actual eye blink takes less than ...

blondel
another name for an apostilb. Proposed in 1942, this unit honors the French physicist André Blondel (1863-1938) for his pioneering work in photometry.

bn
a common symbol for billion, generally the U.S. billion (109).

Board of Trade unit (BOTU)
a British name for the kilowatt hour, a unit of electrical energy.

body inch
an English name for the t'sun , the basic distance measurement used in acupuncture.

body mass index (BMI)
a measure of 'fatness' used in medicine and health. The BMI is equal to a person's mass ('weight') M (in kilograms) divided by the square of his or her height H (in meters): BMI = M/H2. If measurements are made in traditional English units, the equivalent formula is BMI = 703.07•M/H2, where M is me...

boe
abbreviation for 'barrel of oil equivalent,' a commercial unit of energy. One boe is equal to about 6.119 gigajoules (GJ) or 5.800 million Btu.

bohr or bohr radius (a0)
a unit of distance used in particle physics. The bohr radius represents the mean distance between the proton and the electron in an unexcited hydrogen atom. It equals about 52.918 picometers (pm), or 52.918 x 10-12 meter. The unit is named for the Danish physicist Niels Bohr (1885-1962), who explained the structure of atoms i...

boll
a traditional unit of volume in Scotland equal to 16 Scots pecks or 4 firlots. This is about 145 liters for wheat, peas, or beans, or about 194 liters for oats or barley.

bone-dry unit (bdu)
a unit used in the forest products industry to measure bulk products such as wood chips. One bone-dry unit is a volume of wood chips (or whatever) that would weigh 2400 pounds (1.0886 metric ton) if all the moisture content were removed. The bone-dry ton (bdt) is similar but based on a weight of 2000 pounds (0.9072 metric ton). The bone-dry metric ...

bore
the bore of a gun is the inside diameter of its barrel. As a result, 'bore' is sometimes used as a unit, meaning the same as gauge for shotguns and the same as caliber for other guns.

bovate
an old English unit of land area equal to 1/8 hide. This was roughly 15 acres or 6 hectares. The word comes from the Latin bovis, an ox, indicating that the bovate was an area that could be farmed with the help of one ox.

box
a unit of volume, usually informal but standardized in certain industries. In the U.S., a box of citrus fruit contains 1.6 bushels (56.383 liters).

BP
abbreviation for 'years before present,' a unit of time used in anthropology, geology, and paleontology. By international convention, the year 1950 CE (or AD) represents the present, so years 'BP' are really years before 1950.

bpd
abbreviation for barrels per day, a unit of production used in the petroleum industry.

bpm
abbreviation for beats per minute, the common unit of tempo in music. The same symbol is used in medicine for heart rates and also for respiration rates (breaths per minute). Technically, 1 bpm is equal to 1/60 hertz.

braça
see braza, below.

brace
another name for a pair. The word is used mostly by hunters, who may speak of a brace of partridges or a brace of shotguns. Derived from the Latin word bracchia for both arms, it literally means 'one for each arm.'

brake horsepower (bhp)
the effective power output of an engine, sometimes measured as the resistance the engine provides to a brake attached to the output shaft. See horsepower.

breadth
another name for a span (9 inches or 22.86 centimeters). This unit is traditionally used to measure the dimensions of flags.

brewster (B)
a unit used in optics to measure stress-induced birefringence. A material exhibits birefringence if it has different indices of refraction along different axes. Many crystals exhibit birefringence. In addition, certain substances, including many plastics, exhibit birefringence if they are subjected to compression or stress in one direction. The bre...

bright, brightness
a unit describing surface brightness, or reflectivity, especially of paper. The fraction of light reflected by a surface is called its albedo, and its brightness is the albedo expressed as a percentage. Thus '88 bright' paper reflects 0.88, or 88%, of the light falling on the paper.

bril
a unit used to express the 'brilliance' or subjective brightness of a source of light. The scale used is logarithmic: an increase of 1 bril means doubling the luminance (and thus the actual amount of light energy) emitted by the source. A luminance of 1 lambert is defined to have a brilliance of 100 brils. Mathematically, the brilliance in brils eq...

British horsepower (Bhp)
the traditional horsepower, equal to about 745.7 watts, as opposed to the metric horsepower, which is equal to about 735.5 watts. Note that the symbol bhp is also used for brake horsepower.

Btuh
a non-standard symbol used in the U.S. heating and airconditioning industry for British thermal units per hour, a unit of power. 1 Btuh equals 0.293 071 watt. The proper symbol is Btu/h.

bucket
a unit of volume, generally informal. In the U.S., many commodities (both wet and dry) are sold in plastic buckets holding 5 U.S. liquid gallons (about 18.927 liters). In Britain, a bucket is often understood to be 4 gallons, or 18.182 liters based on the British Imperial gallon.