U.S. CUSTOMARY LINEAR MEASURES

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).

1000 mil	= 1 inch	= 2.54 centimeters
12 inches (in)	= 1 foot (ft)	= 30.48 centimeters
3 feet	= 1 yard (yd)	= 0.9144 meter
5-1/2 yards	= 1 rod (rd), pole, or perch	= 16-1/2 ft	= 5.029 meters
40 rods	= 1 furlong (fur)	= 220 yds	= 660 ft	= 0.201 kilometers
8 furlongs	= 1 statute mile (mi)	= 1,760 yds	= 5,280 ft	= 1.609 kilometers
3 statute miles	= 1 league*	= 5,280 yds	= 15,840 ft	= 4.82 kilometers
* 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.

GUNTER'S OR SURVEYOR'S CHAIN MEASURES

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.

7.92 inches	= 1 link (li)	= 20.12 centimeters
25 links	= 1 rod (rd)	= 16-1/2 feet	= 5.029 meters
100 links	= 1 chain (ch)	= 4 rods	= 66 ft	= 20.11 meters
10 chains	= 1 furlong (fur)	= 660 ft	= 0.201 kilometers
80 chains	= 1 statute mile	= 320 rods	= 5,280 ft	= 1.609 kilometers

NAUTICAL MEASURES

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.

6 feet	= 1 fathom	= 1.82 meters
120 fathoms	= 1 cable	= 720 feet	= 219.45 meters
8.44 cables	= 1 International Nautical Mile	= 1.852 kilometers
1.15 statute mi	= 1 Int'l Nautical Mile	= 6,076.11549 feet	= 1.852 kilometers

METRIC LINEAR MEASURES

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 (Syst�m Internationale).

10 millimeters (mm)	= 1 centimeter (cm)	= 0.39 inch
10 centimeters	= 1 decimeter (dm)	= 100 millimeters	= 3.94 inches
10 decimeters	= 1 meter (m)	= 1000 millimeters	= 39.37 inches
10 meters	= 1 dekameter (dam)	= 32.81 feet
10 dekameters	= 1 hectometer (hm)	= 100 meters	= 328.1 feet
10 hectometers	= 1 kilometer (km)	= 1000 meters	= 0.62 mile

Squares and cubes of units are sometimes abbreviated by using "superior" figures. For example, ft2 means square foot, and m3 means cubic meter.

U.S. CUSTOMARY AREA MEASURES

144 square inches	= 1 sq ft (ft2)	= 0.093 sq meter
9 square feet	= 1 sq yd (yd2)	= 1,296 sq in	= 0.836 sq meter
30-1/4 square yards	= 1 sq rd (rd2)	= 272-1/4 sq ft	= 25.29 square meters
160 square rods	= 1 acre	= 4,840 yd2	= 43,560 ft2	= 0.405 hectare
640 acres	= 1 square mile (mi2)	= 2.590 sq kilometers
1 square mile	= 1 section (of land)	= 2.590 sq kilometers
6 square miles	= 1 township*	= 36 sections	= 36 square mi.	= 93.24 sq kilometers
* 6 square miles is a somewhat imprecise measure of a township, but one which is used for many practical purposes. In actuality, the east and west borders follow the meridians, making the north or south border slightly less than 6 miles long due to the curve of the earth.

METRIC AREA MEASURES

100 square millimeters (mm2)	= 1 square centimeter (cm2)	= 0.155 square inch
10,000 square centimeters	= 1 square meter (m2)	= 1,000,000 mm2	= 1.19 square yards
100 square meters	= 1 are (a)	= 119.60 square yards
100 ares	= 1 hectare (ha)	= 10,000 m2	= 2.471 acres
100 hectares	= 1 square kilometer (km2)	= 1,000,000 m2	= 0.3861 square miles

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.

U.S. CUSTOMARY LIQUID MEASURES

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.

8 fluid drams	= 1 fluid ounce	= 29.57 milliliters
4 fluid ounces (oz)	= 1 gill	= 0.118 liter
4 gills (gi)	= 1 pint (pt)	= 28.875 in3	= 0.473 liter
2 pints	= 1 quart (qt)	= 57.75 in3	= 0.946 liter
4 quarts	= 1 gallon (gal)	= 231 in3	= 8 pts	= 32 gills	= 3.785 liters

U.S. CUSTOMARY DRY MEASURES

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.

2 dry pints (pt)	= 1 dry quart (qt)	= 67.2006 in3	= 1.101 liters
8 dry quarts	= 1 peck (pk)	= 537.605 in3	= 16 pt	= 8.81 liters
4 pecks	= 1 bushel (bu)*	= 2,150.42 in3	= 32 dry qt	= 35.239 liters
* 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.

APOTHECARIES' FLUID MEASURES

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.

60 minims (min)	= 1 fluid dram (fl dr)	= 0.2256 in3	= 3.888 grams
8 fluid drams	= 1 fluid ounce (fl oz)	= 1.8047 in3	= 31.103 grams
16 fluid ounces	= 1 pint (pt)	= 28.875 in3	= 128 fl drs	= 0.473 liter
2 pints	= 1 quart (qt)	= 57.75 in3	= 32 fl oz	= 256 fl drs	= 0.946 liter
4 quarts	= 1 gallon (gal)	= 231 in3	= 128 fl oz	= 1,024 fl drs	= 3.785 liters

U.S. COOKING MEASURES

76 drops	= 1 teaspoon	= 1-1/3 fl drams	= 4.9288 milliliters
3 teaspoons	= 1 tablespoon	= 4 fl drams	= 14.786 milliliters
16 tablespoons	= 1 cup	= 8 fl ounces	= 0.2366 liter
2 cups	= 1 pint	= 16 fl ounces	= 0.4732 liter
2 pints	= 1 quart	= 32 fl ounces	= 0.9463 liter

BRITISH IMPERIAL LIQUID AND DRY MEASURES

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.

British imperial		cubic inches	U.S. equiv.	Metric
60 minims	= 1 fluidram (fl dr)	= 0.216734 in3	= 0.961 fl dr	= 3.552 milliliters
8 fluidrams	= 1 fluidounce (fl oz)	= 1.7339 in3	= 0.961 fl oz	= 28.412 milliliters
5 fluidounces	= 1 gill	= 8.669 in3	= 4.805 fl oz	= 142.066 milliliters
4 gills	= 1 pint	= 34.678 in3	= 1.201 fl pt	= 0.5683 liters
2 pints	= 1 quart	= 69.355 in3	= 1.201 fl qt, 1.032 dry qt	= 1.136 liters
4 quarts	= 1 gallon	= 277.420 in3	= 1.201 fl gal	= 4.546 liters
2 gallons	= 1 peck	= 554.84 in3	= 1.0314 pecks	= 9.087 liters
4 pecks	= 1 bushel	= 2219.36 in3	= 1.032 bushels	= 36.369 liters

METRIC MEASURES OF CAPACITY

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.

10 milliliters (ml)	= 1 centiliter (cl)	= 0.338 fluid ounce
10 centiliters	= 1 deciliter (dl)	= 100 milliliters	= 0.21 pint
10 deciliters	= 1 liter (l)	= 1000 milliliters	= 1.057 quarts
10 liters	= 1 dekaliter (dal)	= 2.6417 gallons
10 dekaliters	= 1 hectoliter (hl)	= 100 liters	= 26.417 gallons
10 hectoliters	= 1 kiloliter (kl)	= 1,000 liters	= 264.17 gallons

U.S. CUSTOMARY CUBIC MEASURES

1,728 cubic inches (in3)	= 1 cubic foot (ft3)	= 0.028 cubic meter
27 cubic feet	= 1 cubic yard (yd3)	= 0.765 cubic meter

METRIC

1,000 cubic millimeters (mm3)	= 1 cubic centimeter (cm3)	= 0.061 cubic inch
1,000 cubic centimeters	= 1 cubic decimeter (dm3)	= 61.023 cubic inches
1,000 cubic decimeters	= 1 cubic meter (m3)	= 1 stere	= 1.307 cubic yards

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.

27-11/32 grains	= 1 dram (dr)	= 1.1772 grams
16 drams	= 1 ounce (oz)	= 437-1/2 grains	= 28.35 grams
16 ounces	= 1 pound (lb)	= 256 drams	= 7,000 grains	= 0.454 kilogram
100 pounds	= 1 hundredweight (cwt)*	= 45.359 kilograms
112 pounds	= 1 gross or long hundredweight (cwt)*	= 50.802 kilograms
20 hundredweights	= 1 short ton (tn)	= 2,000 lbs*	= 0.907 metric ton
20 gross or long hundredweights	= 1 gross or long ton	= 2,240 lbs*	= 1.016 metric tons
*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.

24 grains (gr)	= 1 pennyweight (dwt)	= 1.555 grams
20 pennyweights	= 1 ounce troy (oz t)	= 480 grains	= 31.103 grams
12 ounces troy	= 1 pound troy (lb t)	= 240 dwt	= 5,760 gr	= 0.373 kilogram

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.

20 grains (gr)	= 1 scruple (s ap)	= 1.296 grams
3 scruples	= 1 dram apothecaries' (dr ap)	= 60 gr	= 3.888 grams
8 drams apothecaries	= 1 ounce apothecaries' (oz ap)	= 24 s ap	= 480 gr	= 31.103 grams
12 ounces apothecaries	= 1 pound apothecaries' (lb ap)	= 96 dr ap	= 373.24 grams	= 288 s ap	= 5,760 grains

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.

10 milligrams (mg)	= 1 centigram (cg)	= 0.154 grain
10 centigrams	= 1 decigram (dg)	= 100 milligrams	= 1.543 grains
10 decigrams	= 1 gram (g)	= 1,000 milligrams	= 0.035 ounce
10 grams	= 1 dekagram (dag)	= 0.353 ounce
10 dekagrams	= 1 hectogram (hg)	= 100 grams	= 3.527 ounces
10 hectograms	= 1 kilogram (kg)	= 1,000 grams	= 2.2046 pounds
1,000 kilograms	= 1 metric ton (t)	= 1.102 short tons

acre
A measure of area, used for surveying land. One acre is equal to 160 square rods or 43,560 square feet. The term originally referred to the area of land a yoke of oxen (two oxen) could plow in one day.

agate
A measure used in printing, especially for classified advertising, equivalent to 1/14 inch. An agate line is a space one column wide and 1/14 inch deep (1/14 of a column inch). Originally, a measure of type size of 5-1/2 points. See also point.

ampere (Amp)
A unit of electrical current in electrons per second. Equivalent to a flow of one coulomb per second or to the steady current produced by the pressure of one volt applied across a resistance of one ohm. See also ohm; volt.

assay ton (AT)
A unit of weight used in assaying. One assay ton is equal to 29.167 grams. The relationship between one assay ton to one milligram is the same as one net ton (2,000 pounds avoirdupois) to one ounce troy. Therefore, the weight in milligrams of precious metal from one assay ton gives the number of troy ounces to the net ton.

bale
An imprecise measure of a large bundle of goods, especially cotton or hay. The weight varies from country to country. In the U.S., the approximate weight of a bale of cotton is 500 pounds, while in Egypt it is approximately 750 pounds.

barrel (bbl)
A measure of volume, which varies according to the commodity, and can also vary from state to state. A barrel can be either a wet or dry volume measure. One barrel is generally between 31 and 42 gallons. One barrel of fermented liquors often means 31 gallons, one barrel of liquid is often 31-1/2 gallons, on barrel of beer is often 36 gallons, one barrel of "proof spirits" is 40 gallons by U.S. federal law, and one barrel of crude oil for statistical purposes is generally 42 gallons. 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 in3 = 3.281 bushels, struck measure. 1 barrel, standard, cranberries = 86-45/64 dry quarts = 5,826 in3 = 2.709 bushels, struck measure. board foot (fbm, BF, bd ft) A unit of measurement used for lumber. One board foot is 12 inches by 12 inches by 1 inch, or one square foot of lumber one inch thick. Rough lumber is often sold by the board foot.

bolt
A unit of measurement used for fabric. One bolt is 40 yards long.

British thermal unit (Btu)
A unit used to describe heating capacity. One Btu is the amount of energy needed to raise the temperature of one pound of water one degree Fahrenheit. 1 Btu = 252 Calories. See also calorie.

caliber
A unit for measuring the diameter of the bore of a gun. In the U.S. and Britain, this has traditionally been expressed in hundredths or thousandths of an inch and written as a decimal fraction (i.e., .22 or .465). It has become more common for caliber to be expressed in millimeters. Naval gun caliber is the number by which one multiplies the bore diameter to find the barrel length.

caliper
A unit used to measure the thickness of paper or board. One caliper is equal to one mil, or 1/1,000 of an inch.

calorie
A measurement of heat used in place of British thermal units (Btu) by countries using the metric system. One small calorie is the amount of energy needed to raise the temperature of one gram of water by one degree Celsius, from 14.5�C to 15.5�C, or 4.1840 joules. One big calorie (kilocalorie) = 1,000 small Calories. See also British thermal unit; joule.

carat
A unit for measuring the weight of precious stones. One international carat is 200 milligrams (approximately 3.086 grains). Originally, a carat was the weight of a locust tree seed, about 1/142 of an ounce. See also karat.

cord
A unit of volume used for firewood. One cord is a stack of wood that measures 8 feet by 8 feet by 2 feet, or 128 cubic feet. A face cord (or short cord) is a stack of logs measuring 8 feet by 4 feet by whatever the length of the logs happens to be.

cubit
An ancient unit of length 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.

decibel
Not an actual unit of measurement, but a comparison between one sound an another to show the level of a sound's energy. 0 decibels is the softest sound audible to the human ear, and 130 decibels is painful to the human ear. The decibel scale is logarithmic, so that a 10 decibel increase doubles the loudness.

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 figuring 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.

ell
A unit of length used for measuring fabric. An English term, an ell is 45 inches, or 1/32 of a bolt. Bolts of fabric are often sold in the United States and England in 45 inch widths. See also bolt.

em
A unit of length used in printing. An em is equal to the point size of the type in use, that is, a 6-point em is 6 points wide. An en is equal to one half of an em. Nut is another printer's term for an en.

freight ton (also called measurement ton)
A unit of volume used most often for sea freight. One freight ton is usually equal to 40 cubic feet of merchandise. A freight ton may also refer to a unit of volume for freight that weighs one ton, varying depending on the commodity.

gauge
A measure of shotgun bore diameter. Gauge numbers originally were determined by finding the number of lead balls with a diameter equal to that of the bore that made up a pound (i.e., a 12 gauge shotgun), so that the smaller the gauge number, the bigger the shotgun bore. Today an international agreement assigns millimeter measures to each gauge. See also caliber.

great gross
A numerical figure used for counting commercial items. One great gross is a dozen gross, or 1,728 items. See also gross.

gross
A numerical figure used for counting commercial items. One gross is a dozen dozen, or 144 items. See also great gross.

hand
A unit of length, usually used for measuring horses at withers. One hand is 4 inches or 10.16 cm. It was derived from the width of the hand.

hertz
Measurement unit for the frequency of electromagnetic waves. One hertz is equal to one cycle per second.

hogshead (hhd)
A liquid measurement for a large cask or barrel. One hogshead is 63 U.S. gallons, or 238 liters. A hogshead may also refer to a large cask containing anywhere from 63 to 140 gallons.

horsepower (hp)
A unit used to measure 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. See also British thermal unit, Watt.

joule
A unit of energy. One joule is equal to the amount of work done by a force of one newton when its point of application moves through a distance of one meter in the direction of the force.

karat
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. 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.

knot
A rate of travel used to measure a ship's speed, but also used for airplanes and other vehicles. One knot is the rate of one nautical mile (1,852 meters) per hour.

league
A unit of distance. One league is usually estimated at 3 statute miles in English-speaking countries, but it can range anywhere from about 2.4 to 4.6 statute miles. The league was originally a Gaulish unit of distance equal to 1.5 Roman miles.

light-year
A unit of distance used by astronomers. One light year is 5,880,000,000,000 miles, which is the distance light travels in a vacuum in a year at the rate of 186,281.7 miles (299,792 kilometers) per second.

magnum
A unit of volume for liquid, most often for wine. A magnum is not a precise unit, but may refer to 1.5 liters, 2/5 of a gallon or two quarts. It also refers to the bottle itself.

ohm
A unit of electrical resistance which slow the flow of amps. A circuit in which a potential difference of one volt produces a current of one ampere has a resistance of one ohm. See also ampere; volt.

parsec
A unit of measure used by astronomers. One parsec is approximately 3.26 light-years or 19.2 trillion miles. The term is derived from a combination of first syllables of parallax and second. A parsec is the distance is a distance having a heliocentric parallax of one second (1/3600 degree). See also light-year.

pi (�)
The ratio of the circumference of a circle to its diameter. The value of pi is approximately 3.1416.

pica
A unit of length used in printing to describe the width of a line of type. One pica is usually calculated as 1/6 inch or 12 points. See also point.

pipe
A unit of liquid measure, most often used for wine or oil. One pipe is equal to two hogsheads, or 126 gallons. See also hogshead.

point
A unit of measurement for the height of type in printing. One point is approximately .013837, 1/72 inch, or 1/12 pica. Used in printing for measuring type size. Originally one point was 1/72 of a French inch. European and American point sizes are slightly different. A point can also a unit of measurement used in printing and binding equal to 1/1,000 of an inch. See also pica.

ream
The numerical unit used for measuring pieces of paper. One ream is 20 quires, which is now usually 500 sheets, but can be 480 sheets, and occasionally is 516 sheets of paper.

register tons
A unit of volume, and not weight, used to express the total capacity of a ship, called gross register tonnage, gross tonnage, or gross weight. One register ton is equal to 100 cubic feet. Most often used for passenger ships, but may be applied to other types of ships.

roentgen
An unit to measure radiation exposure produced by X-rays. One roentgen is equal to the amount of radiation produced in one cubic centimeter of dry air at 0�C and standard atmospheric pressure ionization equal to one electrostatic unit of charge.

score
A numerical figure. One score is 20 units.

sound, speed of
A rate of speed, which varies depending on temperature, altitude and the media through which the sound is traveling. In general terms, the "speed of sound" is usually placed at 1,088 feet per second, or about 750 miles per hour at 32�F at sea level.

span
A British unit of length, now little used. One span is equivalent to 9 inches or 22.86 cm. It is derived from the distance between the end of the thumb and the end of the little finger of a spread hand.

square
A unit of square measure used in the building trade. One square is equal to 100 square feet. It often refers to roofing materials.

stone
A unit of weight still in use in the United Kingdom. One stone is equal to 14 pounds avoirdupois, or approximately 6.3 kilograms.

therm
A unit of heat, although it may be defined in different ways. One therm is equal to 100,000 Btu's or to 1,000 large calories. See also British thermal unit; calorie.

ton mile
(shipping) The transport of one ton of cargo for one mile. Used most often in air cargo services.

township
A unit of land measurement used in the U.S. One township is almost 36 square miles. The south border is 6 miles long. The east and west borders, also 6 miles long, follow the meridians, making the north border slightly less than 6 miles long.

tun
A unit of liquid measurement, used for wine and other liquids. One tun is equal to two pipes, or four hogsheads, or 252 gallons. In practice a tun may be more than 252 gallons. See also hogsheads; pipes.

volt
A measure of electrical potential difference. Volts are the pressure that moves the amps along a wire. Normal household voltage in the U.S. is 120 volts.

watt
A unit of power which is a measure of the amount of work an appliance is capable of. A watt is the power used by a current of one ampere across a potential difference of one volt.