Many of these measures are based on those developed in medieval England, when a yard was a measure of King Edward I's waist, a rod was an actual 10-foot pole and a furlong was the width of 32 plowed rows. The mile began with the Romans measuring it as 1,000 paces. The United States is one of the few countries which still uses many of them. Our yard is now officially 3600/3937 of a meter (exactly 0.9144 meter), while a survey foot is 1200/3937 of a meter (approximately 0.3048 meter).

* A league is an imprecise measure that may range from approximately 2.4 to 4.6 statute miles, but in most English-speaking countries it refers to 3 statute miles.

These measures are based on a 17th century British surveyor's tool that was, in fact, a 66-foot long chain composed of 100 links. They fit in with the rod and furlong already in use.

A nautical mile is based on the circumference of the earth, but the precise definition of it has varied considerably through the centuries. Most recently, a nautical mile has meant a minute (1/60) of a degree. The current International Nautical Mile, defined in 1929 and adopted by U.S. in 1954 is slightly shorter than the U.S. Nautical Mile, which is no longer used.

A meter is the length of the path traveled by light in a vacuum during the time interval of 1/299,794,458 second. Originally, it was one 10-millionth of a line running from the equator, through Paris to the North Pole. The metric system is also called SI (Systèm Internationale).

Squares and cubes of units are sometimes abbreviated by using "superior" figures. For example, ft 2 means square foot, and m 3 means cubic meter.

U.S. CUSTOMARY AREA MEASURES

* 6 square miles is a somewhat imprecise measure of a township, but one which is used for many practical purposes. In actuality, a township is 6 miles on each of its east and west borders which follow the meridians, making the north or south border slightly less than 6 miles long due to the curve of the earth.

The American method of measuring volume is based on an Ancient Egyptian measure, a 12th century British measure and a custom of doubling each measure to find the next. Some measures dropped along the way, so this is no longer apparent. There are two official sets of volume measures in the U.S., wet and dry.

The gallon is now officially defined in terms of cubic inches, which, in turn, are defined in terms of the meter. When necessary to distinguish the liquid pint or quart from the dry pint or quart, the word "liquid" or the abbreviation "liq" should be used in combination with the name or abbreviation of the liquid unit.

The bushel is now officially defined in terms of cubic inches, which, in turn, are defined in terms of the meter. When necessary to distinguish the dry pint or quart from the liquid pint or quart; the word "dry" should be used in combination with the name or abbreviation of the dry unit.

* This is also called a bushel, struck measure. One bushel, heaped measure is frequently recognized as 1-1/4 bushels, struck measure. More precisely, one bushel, heaped is equal to 1.278 bushels, struck.

These units were once widely used in the U.S. for pharmaceutical purposes, but have largely been replaced by metric units. These measures are actually the same as those for U.S. customary wet measure (above), with some additional subdivisions.

The British changed their definitions of capacity measures slightly in the 19th century, so that British Imperial measures having the same names as U.S. measures are slightly larger than their U.S. counterparts.

The liter was derived from the kilogram, originally the volume occupied by a kilogram of water. It is now officially defined as a cubic decimeter of pure water, which is nearly the same. This one set of measures is used for all capacity measures.

METRIC

When necessary to distinguish avoirdupois units from troy or apothecaries' units, the word "avoirdupois" or the abbreviation "avdp" should be used in combination with the name or abbreviation of the unit.

AVOIRDUPOIS WEIGHT

This is the weight system in everyday use in the U.S. Historically, it is a rearrangement of the troy system. The word avoirdupois is French, meaning goods of weight. The avoirdupois pound is now officially defined as 0.45359237 kilogram.

*When the terms "hundredweight" and "ton" are used unmodified, they are commonly understood to mean the 100-pound hundredweight and the 2,000-pound (short) ton, respectively; these units may be designated "net" or "short" when necessary to distinguish them from the corresponding units in gross of long measure.

TROY WEIGHT

The troy system began in Ancient Egypt and was modified over the years by Europeans. The British used the troy as the official weight system for currency, while the U.S. mint adopted it in America. These units are still used for over-the-counter sales of precious metals, although they have largely fallen into disuse, in favor of the metric system.

APOTHECARIES' WEIGHT

While one pound apothecaries' is equivalent to 1 pound troy, the apothecaries' system differs in its subdivisions. These units were once widely used in the United States for pharmaceutical purposes, but have largely been replaced by metric units, although they are still legal standards.

METRIC WEIGHT (MASS)

A kilogram was originally defined as the mass of one cubic decimeter of water at the temperature of maximum density, but is now a cylinder of platinum-iridium alloy of the same size.

apothecary weights
A variation of the traditional English troy weight system formerly used by apothecaries (pharmacists). Apothecary weights use the troy pound (of 5760 grains) which is divided into 12 ounces (of 480 grains each). Apothecary weights, however, divide the ounce into 8 drams (of 60 grains each), and each dram into 3 scruples (of 20 grains each). The apothecary weight system has been replaced by metric units.

ASA number
Acronym for American Standards Association number. A unit of measurement of the exposure speed of photographic film emulsion. ASA 200 film is therefore exposed at twice the speed of ASA 100 film. The ASA film exposure rating system has been largely combined with the DIN (Deutsches Institut für Normung) rating system in a new ISO (International Standards Organization) composite rating (e.g., ISO 200/24º).

avoirdupois weights
A system of weight measurement based on a pound (of 7,000 grains) divided into 16 ounces and used in most all English-speaking countries of the world. Also called the Imperial System of Weights and Measurement. Avoirdupois is French for "goods having weight" meaning that the goods were offered for sale based on weight rather than by the piece or by volume.

baht
(a) The currency of Thailand. (b) A traditional Thai unit of weight measurement for precious metals now equal to 15 grams. (c) "Baht chain" is gold necklace chain that is almost pure (22-24 karat) gold sold in Thailand in units of 15 grams. A three-baht chain weighs 45 grams.

bale (bl)
An imprecise measure of a large bundle of goods, especially cotton or hay. The weight varies from country to country and by commodity. In the U.S., a bale of cotton weighs between 480 and 500 pounds, while in Egypt a bale of cotton weighs 720 to 750 pounds.

barrel (bbl/brl/bl/bo)
A unit of liquid or dry volume measurement which varies by commodity, and sometimes by country. A barrel is generally between 31 and 42 gallons. One barrel of fermented liquors is 31 gallons, one barrel of other liquids is typically 31.5 gallons, a barrel of beer is 36 gallons, one barrel of "proof spirits" is 40 gallons by U.S. federal law, and one barrel of crude oil (abbreviation is `bo') for statistical purposes is 42 gallons (159 liters). Two common barrel measurements for dry commodities are:
1 barrel, standard for fruits, vegetables, and other dry commodities (except cranberries) = 105 dry quarts = 7,056 in 3 = 3.281 bushels, struck measure.
1 barrel, standard, cranberries = 86-45/64 dry quarts = 5,826 in 3 = 2.709 bushels, struck measure.

bell
A unit of time measurement used traditionally on sailing ships and equal to one-half hour. A "watch" is the standard period of time a sailor is on duty and is divided into 8 bells or 4 hours. During a watch each half hour is marked by a sounding of the bell: 30 minutes, 1 bell; 1 hour, two bells, etc.

carat (ct or c)
(a) A unit of weight or mass measurement of precious stones equal to 200 milligrams (approximately 3.086 grains). Originally, a carat was the weight of a locust tree seed, about 1/142 of an ounce. (b) Alternate spelling in the U.K. for the U.S. karat, a measure of the purity of gold in an alloy. See also karat.

catty
A traditional unit of weight measurement in East and Southeast Asia equal to 4/3 pounds avoirdupois. In Malaysia the catty is still equal to 4/3 pounds. In Thailand the catty is now equal to precisely 600 grams (0.6 kilo).

cubit
An ancient unit of linear measurement based on the length of the forearm, from the elbow to the tip of the middle finger. One cubit is not a precise length, although it is usually figured between 17 and 21 inches, and most often at 18 inches.

dan or tan
(a) A traditional Chinese unit of weight or mass measurement equal to 100 cattys or 1,600 taels. (b) A modern Chinese unit of weight or mass measurement equal to 50 kilograms or 100 jin.

displacement ton
A unit used for measuring the weight of water displaced by a ship, in place of weighing the ship itself. One displacement ton is equal to a long ton, or 2,240 pounds. It is calculated by finding the number of cubic feet of water displaced and calculating the weight of the water. Loaded displacement tonnage refers to the displacement tonnage of a ship when it is carrying its usual cargo, fuel and crew load. Light displacement tonnage is the displacement tonnage of an unloaded ship, while the dead weight tonnage is the weight that the ship can carry, or the difference between the loaded displacement and the light displacement tonnage. Different types of ships are more commonly described according to one type of displacement tonnage or another.

deadweight ton (dwt)
A term used to express the total carrying capacity of a vessel expressed in long tons of 2,240 pounds. Specifically, the deadweight tonnage of a vessel is its loaded displacement minus its light displacement. This is the vessel's capacity for cargo, fuel, supplies, passengers and crew. In modern usage the metric ton of 2,204.623 pounds is often used instead of the long ton.

DIN number
Acronym for Deutsches Institut für Normung (a German standards agency) number. A unit of measure of the exposure speed of photographic film emulsion. DIN 24º (with a degree symbol) is equal to ASA 200. A difference of 3 in the DIN system doubles (or halves) the film speed rating. Therefore DIN 27 is equal to ASA 400. The DIN film exposure rating system has been largely combined with the ASA (American Standards Association) rating system in a new ISO (International Standards Organization) composite rating (e.g., ISO 200/24º).

fathom (fth or fath)
A unit of linear measurement equal to 6 feet or two yards. The term comes from fæthm, Old English for outstretched arms, meaning the distance between a man's outstretched arms. The fathom is used almost exclusively in shipping as a measurement of the depth of water. Many other cultures have used this form of measurement unit (with slightly different values). They include braza (Spanish), toise (French), klafter (German), favn (Dutch), famn (Swedish) and ken (Japanese).

FEU
Acronym for 40-foot equivalent unit. A unit of cargo capacity equal to one (1) forty-foot ocean cargo container (40' x 8' x approximately 8.5'). The term is used to quantify the carrying capacity of a container ship or the throughput volume of a port facility.

freight ton (FT)
(a) (modern usage) A unit of weight or mass measurement equal to one metric ton (1,000 kilograms) of freight of any volume. (b) (outdated usage) A unit of volume equal to 40 cubic feet, used to measure the cargo or cargo capacity of a ship, truck, railcar or airplane. Also called a measurement ton.

glass
A traditional unit of time measurement based on the use of an hourglass or sandglass. A "glass" was equal to the time it took sand to pass from the top to the bottom of the specially-designed glass vessel. The amount of time measured could be controlled by varying the width of the passageway from the top to the bottom, or by adding or subtracting sand. The most traditional instrument was the hourglass and was calibrated to measure one (1) hour. At sea, half-hourglasses were often used to correspond to the ship's bell time measurement in units of one-half hour.

GMT
Acronym for Greenwich Mean Time. GMT is the designation for the standard time at longitude 0º which runs north and south and passes through the Royal Observatory at Greenwich England. Longitude 0º is also called the Prime Meridian. The usage of the term Universal Time or UT instead of GMT has come into vogue recently.

gongli
A modern Chinese unit of linear measurement equal to two li, or 1 kilometer and often referred to as the metric li.

grain
(a) A unit of weight or mass measurement equal to 1/60 dram or 1/7000 pound (64.799 milligrams). (b) A unit of weight or mass measurement used for weighing pearls and precious stones equal to 1/4 carat (50mg). (c) Historically, the weight of a single grain of wheat taken from the middle of the ear.

great gross
A unit of quantity for counting commercial items typically sold at wholesale equal to a dozen gross (12 x 144) or 1,728.

gross
A unit of quantity for counting commercial items typically sold at wholesale equal to 144.

hank
(a) A coil of rope, wool or yarn. (b) A length of textile material whose length varies depending upon the material. A hank of wool is 560 yards, of cotton or silk is 840 yards, linen 300 yards, tapestry wool 55 meters and crewel wool approximately 180 meters. (c) A number of stands of pearls, beads or other strung gem or jewelry material that have been tied together at the end to form a unit to be sold wholesale. 

horsepower (hp)
A unit of measure for the power of engines. One horsepower is equal to 746 watts or to 2,546.0756 Btu per hour. It was derived from the power needed by a horse to lift 33,000 pounds a distance of 1 foot in 1 minute or to lift 550 pounds 1 foot in 1 second.

imperial gallon (IG)
A unit of volume measurement based on the British Imperial System equal to 1.201 U.S. liquid gallons or 4.546 liters.

imperial units
Unit designations for the British Imperial System of weights and measures as adopted by the British Parliament in 1828. The major units of the British Imperial System are the foot of 12 inches, the pound avoirdupois of 16 ounces and the imperial pint.

international nautical mile
A unit of distance measurement used in nautical and aeronautical navigation equal to the average distance on the earth's surface of one (1) minute of latitude. Because the Earth is not a perfect sphere this definition left the precise measurement of a nautical mile open to interpretation. As a result there were several competing definitions, including: the Admiralty Mile of 6,080 feet (1,853.18 meters), and the U.S. Nautical Mile of 6080.20 feet (1853.24 meters) (the latter was in use until 1954). However, an international conference held in Monaco in 1929 defined the nautical mile at exactly 1852 meters (6,076.11 feet or 1.1508 statute miles). This is now called the international nautical mile and is the accepted definition.

international unit (IU) (system)
An internationally accepted system for the measurement of drugs and vitamins based upon their level of biological effect (potency) rather than their weight or volume. By agreement, for each substance to which the IU system applies, there is an established biological effect associated with a dose of 1IU of that drug or vitamin. For example, 1IU of Vitamin C is 50 micrograms (0.05mg), while 1IU of a preparation of penicillin is 0.6 microgram.

ISO
Acronym for International Organization for Standardization. The ISO, established in 1947, is a worldwide federation of national bodies, representing approximately 90 member countries that set international standards for everything from the quality grading of steel; for testing the strength of woven textiles; for storage of citrus fruits; for magnetic codes on credit cards; for the exposure speed of photographic film; and for ensuring the quality and performance of such products as surgical implants, ski bindings, wire ropes, and photographic lenses.
International Standardization Organization, 1 rue de Varembé, PO Box 56, CH-1211 Geneva 20, Switzerland; Tel: [41] (22) 749-0111; Fax: [41] (22) 733-3430; Web: www.iso.ch. In the United States contact: International Organization for Standards, The American National Standards Institute, 25 West 43rd Street, 4th Floor, New York, NY 10036 USA; Tel: [1] (212) 642-4900; Fax: [1] (212) 398-0023; Web: www.ansi.org.

jin (sometimes chin or gin)(historic)
A traditional Chinese unit of weight or mass measurement originally equal to 4/3 pounds. The jin was divided into 16 liang.
(contemporary) A Chinese unit of weight or mass measurement equal to 500 grams or 0.5 kilograms and divided into 10 liang.

jo
A traditional Japanese unit of area measurement equal to a tatami mat which is 90cm x 180cm (35.46 inches x 70.92 inches). In area a jo is equal to 1.62 m 3 or 1.94 square yards. The jo is used to describe the area of an apartment or house.

karat (k)
A measure of the purity of gold in an alloy. Each karat represents a ratio of 1/24 purity, indicating how many parts out of 24 are pure. Therefore, 24 karat gold is pure, while 18 karat gold is 3/4 gold and 1/4 alloy. The system was derived from a time when a karat was used to describe 1/24 of a troy pound and 24 karat was one full troy pound. In the U.S. the abbreviation for karat is k. In the U.K. the word is spelled carat just as in carat weight of precious stones and the abbreviation for both is c.

ken
A traditional Japanese unit of length measurement equal to 1.818 meters (5.965 feet) and comparable to the English fathom. One (1) ken equals 6 shaku. The Japanese nautical equivalent of the ken is the hiro .

knot (kn or kt)
A unit of speed (velocity) equal to one nautical mile per hour (1.852 kilometers/hour or 1.1508 miles/hour). The term is used primarily for vessels at sea and airplanes in flight. The usage "knots per hour" is incorrect. Also, a knot is not a nautical mile (distance), but rather a measure of speed. The term knots is derived from the traditional practice of measuring a ship's speed at sea using a cord with evenly-spaced knots called a log line.

koku
A traditional Japanese unit of volume measurement equal to 180.391 liters (39.68 British imperial gallons or 6.37 cubic feet). The koku was originally a measure of the amount of rice required to feed an adult person for a year.

kommerzlast
German for "commercial load." The traditional value of the term varied depending upon the commodity. In modern usage the term is defined as 3 metric tons (tonnes) or 3,000 kilograms total.

last
(a) Traditional German term meaning "load" as in a cart or truckload of a commodity. (b) A traditional unit of weight or mass measurement equal to approximately 4,000 pounds.

li
A traditional Chinese unit of linear measurement whose value varied from 1,760 to 2,115 feet. In modern China the li is 0.5 kilometers (500 meters or 1,640.5 feet). The often misquoted Confucian proverb "A journey of a thousand miles starts with a single step" is actually "A journey of a thousand li starts with a single step."

liang
A traditional Chinese unit of weight or mass measurement that was equal to 1/16 catty (0.5 pound), the same as a tael.
In modern China, the liang equals 50 grams (1/10 jin or 10 quin).

livre
A traditional French and Greek unit of weight or mass measurement equal to 2 marcs or 16 onces. The traditional value of a livre varied from market to market, but was standardized in the 14th century at about 489.5 grams (1.079 pounds) and called the livre poids de marc or livre de Paris.
In modern France, the livre is defined as 500 grams or (0.5 kilogram or 1.1023 pounds).

long ton
A unit of weight or mass measurement equal to 2,240 pounds. Synonomous with the British ton.

measurement ton (MTON or MT)
A unit of cargo-carrying capicity of a cargo vessel, railcar, truck or other cargo conveyance equal to 40 cubic feet (1.1326m 3 ) of cargo capacity. In some usage this is called a freight ton. However, modern convention is to use freight ton when referring to one (1) metric ton (1,000 kilos) of freight.

metric ton (t or MT)
A unit of weight or mass measuremeant equal to 1,000 kilos. Metric ton and tonne are synonomous. In the U.S. the term metric ton is used.

nautical mile (nmi, naut mi or NM)
A unit of distance measurement used in nautical and aeronautical navigation equal to the average distance on the earth's surface of one (1) minute of latitude. Because the Earth is not a perfect sphere this definition left the precise measurement of a nautical mile open to interpretation. As a result there were several competing definitions, including: the Admiralty Mile of 6,080 feet (1,853.18 meters), and the U.S. Nautical Mile of 6080.20 feet (1853.24 meters) (the latter was in use until 1954). However, an international conference held in Monaco in 1929 defined the nautical mile at exactly 1852 meters (6,076.11 feet or 1.1508 statute miles). This is now called the international nautical mile and is the accepted definition.

net ton (NT)
(a) Alternate term used to signify a U.S. short ton (2,000 pounds). (b) Alternate term used to signify a register ton (100 cubic feet of cargo or cargo space on board a vessel). As a result of the possible confusion it is advised that the terms short ton or register ton be used instead of net ton.

qian
A traditional Chinese unit of weight or mass measurement equal in modern usage to 0.1 liang or 5 grams.

ream (rm)
(modern) Five hundred (500) sheets of paper.
(historic) Four hundred and eighty (480) sheets of paper (specifically 20 quires of 24 sheets each).

register ton (RT)
A unit of ocean shipping cargo capacity equal to 100 cubic feet. Also called the merchant marine ton. Note: the register ton abbreviation `RT' is also used for refrigeration ton and revenue ton. 

revenue ton (tonne) (RT)
A revenue-generating cargo shipment of either one (1) metric ton (tonne) or one (1) cubic meter (m 3 ) whichever yields the greatest amount of revenue for the carrier. Revenue ton is a shipping industry billing unit and is usually used in the term revenue ton mile.

revenue ton mile
(a) The shipment of one ton of revenue-generating cargo for one mile. (b) The shipment of one (1) revenue ton of cargo for one mile.

Riga last
A British unit of volume equal to 80 cubic feet (2.265m3) of square-sawn timber or 65 cubic feet (1.841m 3 ) of round (unsurfaced) timber. Named for Riga, the capital of Latvia which was a major port used for the export of Russian timber. Traditionally, a `last' is a unit of mass or volume equal to 4,000 pounds, very close to the weight of 80 cubic feet (2.265m3) of square-sawn timber.

score
A unit of quantity equal to 20.

short ton (st or tn)
A unit of weight or mass measurement equal to 2,000 pounds.

skein
a) A coil of yarn or cord. (b) One sixth (1/6) of a hank.
The length of a skein depends upon the fiber and manufacturer.

stone
A traditional British unit of weight or mass measurement equal to 14 pounds avoirdupois (6.3 kilograms).

tael or tahil
A traditional unit of weight or mass measurement used in eastern Asia with different values depending upon the country or market of use. One tael equals 16 cattys. During the colonial period the tael was standardized at 4/3 (1.333) ounce avoirdupois.

tan or dan
(a) (China traditional) A unit of weight or mass measurement equal to 100 cattys or 1,600 taels. (b) (China modern) A unit of weight or mass equal to 50 kilograms or 100 jin.

tatami
(Japan) A unit of area equal to a traditional tatami mat which is 0.5 ken x 1 ken (90cm x 180cm) or 17.5 square feet (1.62m 3 ). This is the traditional and still used method for describing the area of rooms in apartments or homes. Also called the jo.

TEU
Acronym for 20-foot equivalent unit. A unit of cargo capacity equal to one twenty foot ocean cargo container (20' x 8' x approximately 8.5').

ton
(a) (U.S.) A unit of weight or mass measurement equal to 20 hundredweight of 100 pounds each or 2,000 pounds (907.185 kilograms). Also called the short ton. (b) (U.K.) A unit of weight or mass equal to 2,240 pounds (1,016.047 kilograms). Also called the long ton.

ton, metric
A unit of weight or mass measurement equal to 1000 kilograms (2204.623 pounds avoirdupois). The metric ton is now officially called the tonne.

ton, merchant marine
A unit of volume measurement equal to 100 cubic feet (2.8316m 3 ) used in ocean shipping. Also called a register ton.

ton, displacement (DT or dT)
A unit of weight or mass measurement used to measure the volume of water displaced by a vessel, especially warships. The weight of sea water varies, but a displacement ton has been defined to be 35 cubic feet (0.9911m3) of water.

ton, freight (FT)
(a) A unit of volume measurement equal to 40 cubic feet, used to measure the cargo or cargo capacity of a ship, truck, railcar or airplane. Also called a measurement ton. (b) One metric ton of freight of any volume.

tonne (t) / metric ton
A unit of weight or mass measurement equal to 1000 kilograms. Also called a metric ton. The French spelling `tonne' is used to distinguish it from the U.S. short ton and U.K. long ton.

tonneau
(French) (a) A traditional French unit of weight or mass measurement equal to 2000 livres (approximately 979 kilograms or 1.079 U.S. ton). (b) A traditional French unit of volume equal to 42 cubic pieds (approximately 50.84 cubic feet, or 1440 liters). (c) A shipment of 100 cases, or 1,200 bottles of wine.

troy
A traditional English weight system based on a troy pound of 5760 grains. The troy pound was divided into 12 ounces of 480 grains each. The troy ounce was divided into 20 pennyweight of 24 grains each.
Apothecaries used to divide the troy ounce into 8 drams (of 60 grains each) with each dram equal to 3 scruples (of 20 grains each).
Although the troy pound was abolished in 1878 to avoid confusion with the avoirdupois pound (and system) the troy ounce is still used in quoting the market price of precious metals.
The troy weight system was the numeric basis of the still current English monetary system with one (1) English (U.K.) £ (pound) equal to 20 shillings and 12 pence (pennies) to each shilling.

USP unit
Acronym for United States Pharmacopia unit. A unit of weight or mass of a drug or vitamin based upon its expected biological result as established by the U.S. Food and Drug Administration. The United States Pharmacopia is a reference published by the U.S. Pharmacopia Convention describing the properties of medicinal drugs.

wan
(a) A Chinese unit of quantity equal to 10,000. The wan is used as a unit much like the thousand (1,000) unit is used in the West. Therefore, 100 wan is 1,000,000. (b) A Chinese term used to mean an indefinitely large number.

watt
A unit of power measurement (the amount of work an appliance is capable of) equal to the power used by a current of one ampere across a potential difference of one volt.