Below is information about units of measure, including acre, bolt, gross, hertz, knot, light-year, parsec, pi, ream, sound, square, stone, and more.

acre

An area of 43,560 square feet. Originally, the area a yoke of oxen could plow in one day.

agate

Originally a measurement of type size (5¹/2 points). Now equal to ¹/14 inch. Used in printing for measuring column length.

ampere

Unit of electric current. A potential difference of one volt across a resistance of one ohm produces a current of one ampere.

astronomical unit (A.U.)

93,000,000 miles, the average distance of the earth from the sun. Used for astronomy.

bale

A large bundle of goods. In the U.S., the approximate weight of a bale of cotton is 500 pounds. The weight varies in other countries.

board foot (fbm)

144 cubic inches (12 in. × 12 in. × 1 in.). Used for lumber.

bolt

40 yards. Used for measuring cloth.

Btu

British thermal unit. Amount of heat needed to increase the temperature of one pound of water by one degree Fahrenheit (252 calories).

carat (c)

200 milligrams or 3.086 grains troy. Originally the weight of a seed of the carob tree in the Mediterranean region. Used for weighing precious stones.

chain (ch)

A chain 66 feet or one-tenth of a furlong in length, divided into 100 parts called links. One mile is equal to 80 chains. Used in surveying and sometimes called Gunter's or Surveyor's chain.

cubit

18 inches or 45.72 cm. Derived from distance between elbow and tip of middle finger.

decibel

Unit of relative loudness. One decibel is the smallest amount of change detectable by the human ear.

ell, English

1¹/4 yards or ¹/32 bolt. Used for measuring cloth.

freight, ton (also called measurement ton)

40 cubic feet of merchandise. Used for cargo freight.

great gross

12 gross or 1728.

gross

12 dozen or 144.

hand

4 inches or 10.16 cm. Derived from the width of the hand. Used for measuring the height of horses at withers.

hertz

Modern unit for measurement of electromagnetic wave frequencies (equivalent to “cycles per second”).

hogshead (hhd)

2 liquid barrels or 14,653 cubic inches.

horsepower

The power needed to lift 33,000 pounds a distance of one foot in one minute (about 1¹/2 times the power an average horse can exert). Used for measuring power of steam engines, etc.

karat (kt)

A measure of the purity of gold, indicating how many parts out of 24 are pure. For example: 18-karat gold is ³/4 pure. Sometimes spelled carat.

knot

Not a distance, but the rate of speed of one nautical mile per hour. Used for measuring speed of ships.

league

Rather indefinite and varying measure, but usually estimated at 3 miles in English-speaking countries.

light-year

5,880,000,000,000 miles, the distance light travels in a vacuum in a year at the rate of 186,281.7 miles (299,792 kilometers) per second. (If an astronomical unit were represented by one inch, a light-year would be represented by about one mile.) Used for measurements in interstellar space.

magnum

Two-quart bottle. Used for measuring wine, etc.

ohm

Unit of electrical resistance. A circuit in which a potential difference of one volt produces a current of one ampere has a resistance of one ohm.

parsec

Approximately 3.26 light-years or 3.08 × 10¹³ km (1.92 × 10¹³ mi). Term is combination of first syllables of parallax and second, and distance is that of imaginary star when lines drawn from it to both Earth and the Sun form a maximum angle or parallax of one second (¹/3600 degree). Used for measuring interstellar distances.

pi (π)

3.14159265+. The ratio of the circumference of a circle to its diameter. For practical purposes, the value is used to four decimal places: 3.1416.

pica

¹/6 inch or 12 points. Used in printing for measuring column width, etc.

pipe

2 hogsheads. Used for measuring wine and other liquids.

point

.013837 (approximately ¹/72) inch or ¹/12 pica. Used in printing for measuring type size.

quintal

100,000 grams or 220.46 pounds avoirdupois.

quire

Used for measuring paper. Sometimes 24 sheets but more often 25. There are 20 quires to a ream.

ream

Used for measuring paper. Sometimes 480 sheets, but more often 500 sheets.

roentgen

International Unit of radiation exposure produced by X-rays.

score

20 units.

sound, speed of

Usually placed at 1,088 ft. per second at 32°F at sea level. It varies at other temperatures and in different media.

span

9 inches or 22.86 cm. Derived from the distance between the end of the thumb and the end of the little finger when both are outstretched.

square

100 square feet. Used in building.

stone

Legally 14 pounds avoirdupois in the U.K.

therm

100,000 Btus.

township

U.S. land measurement of 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. Used in surveying.

tun

252 gallons, but often larger. Used for measuring wine and other liquids.

watt

Unit of power. The power used by a current of one ampere across a potential difference of one volt equals one watt.