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.
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.
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.
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.
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.
