Gallon

From Encyclopedia Jr, free information reference for Kids

For other uses, see Gallon (disambiguation).

The gallon (abbreviation: gal) is a unit of volume.

There are three definitions in current use:

• U.S. liquid gallon is 231 in³ (exactly) or 128 U.S. fluid ounce (exactly) or 3.785411784 litres
• U.S. dry gallon 4.404 884 L
• Imperial (UK) gallon is 160 imperial fluid ounces (exactly), or 4.54609 L (legally). That is approximately 1.201 US gallons.

The word has also been used as translation for several foreign units of the same magnitude.^{[citation needed]}

The U.S. dry gallon is less commonly used.

The liquid gallons in current use are subdivided into eight pints. A gallon can also be subdivided into four quarts.

[edit] History

At one time, the volume of a gallon depended on what was being measured, and where it was being measured. But, by the end of the 18th century, three definitions were in common use:

• The corn gallon, or “Winchester gallon”, of about 268.8 in³ (4.405 L),
• the wine gallon, or “Queen Anne’s gallon”, which was 231 in³ (3.79 L), and
• the ale gallon of 282 in³ (4.62 L).

The corn or dry gallon was used in the United States until recently for grain and other dry commodities. It is one eighth of the (Winchester) bushel, originally a cylindrical measure of 18½ inches in diameter and 8 inches depth. That made the dry gallon 9¼²·π in³ = 268.80252 in³. The bushel, which like dry quart and pint still sees some use, was later defined to be 2150.42 in³ exactly, making its gallon 268.8025 in³ exactly (4.404 842 803 2 L). In previous centuries there had been a corn gallon of around 271 to 272 cubic inches.

The wine, fluid or liquid gallon is the standard U.S. gallon since the early 19th century. The wine gallon, which some sources relate to the volume occupied by eight medieval merchant pounds of wine, was at one time defined as the volume of a cylinder six inches deep and seven inches in diameter, i.e. 6·3½²·π = 230.90706 in³. It had been redefined during the reign of Queen Anne, in 1706, as 231 in³ exactly (3 × 7 × 11 in³), which is the result of the earlier definition with π approximated to ²²⁄₇. Although the wine gallon had been used for centuries for import duty purposes there was no legal standard of it in the Exchequer and a smaller gallon (224 in³) was actually in use, so this statute became necessary. It remains the U.S. definition today.

The original ratio between corn and wine gallon is 9¼²:6·3½² = 1369:1176, but 268.8:231 is exactly 64:55 or ca. 13:11. This approximation is still applicable, although the ratio of 1.164 115 646 slightly changed to 1.163 647 186 with current definitions (268.8025:231 = 107521:92400 ~= 1344:1165). ^^ In some contexts it is or was necessary to disambiguate between those two U.S. gallons, so “liquid” or “fluid” and “dry” respectively are then added to the name.

In 1824, Britain adopted a close approximation to the ale gallon known as the Imperial gallon and abolished all other gallons in favor of it. Inspired by the kilogram–liter relationship, the Imperial gallon was based on the volume of 10 lb. of distilled water weighed in air with brass weights with the barometer standing at 30 inches of mercury and at a temperature of 62 °F. In 1963, this definition was refined as the space occupied by 10 lb of distilled water of density 0.998 859 g/mL weighed in air of density 0.001 217 g/mL against weights of density 8.136 g/mL. This works out at approximately 4.546 090 3 L (277.441 6 in³). The metric definition of exactly 4.546 09 dm³ (also 4.546 09 L after the liter was redefined in 1964, ca. 277.419 433 in³) was adopted shortly afterward in Canada; for several years, the conventional value of 4.546 092 L was used in the UK, until the Canadian convention was adopted in 1985.

Before and into the 19th century there were also several other gallons in use. Examples:

224 in³ 

standard wine gallon preserved at the Guildhall

231 in³ 

statute of 5th of Queen Anne

264.8 in³ 

ancient Rumford quart (1228)

265.5 in³ 

Exchequer (Henry VII., 1091, with rim)

266.25 in³ 

ancient Rumford (1228)

268.75 in³ 

Winchester, statute 13 + 14 by William III.

271 in³ − 2 spoonfuls 

Exchequer (Henry VII., 1601, E.E.)

271 in³ 

Exchequer (1601, E.), corn

272 in³ 

corn (1688)

277.18 in³ 

coal, statute 12 of Anne

278 in³ 

Exchequer (Henry VII., with copper rim)

278.4 in³ 

Exchequer (1601 and 1602 pints)

280 in³ 

Exchequer (1601 quart)

282 in³ 

Treasury (gallon for beer and ale)

[edit] See also

• Comparison of the Imperial and U.S. customary systems