Gallon

See also: U.S. customary units

The gallon (abbreviation: gal) is a non-SI measurement unit of volume used in the U.S. customary and the Imperial systems of measurement. Historically it has had many different definitions but, as of 2010, there are only three definitions in current use. These are the U.S. liquid gallon and the U.S. dry gallon which are used in the United States and the Imperial gallon which is in unofficial use within the United Kingdom and Ireland and in semi-official use within Canada. The gallon, be it the U.S. or Imperial gallon, is sometimes used in other English-speaking countries as well.

Definitions and divisions

• The U.S. liquid gallon is equal to 3.785412 litres which is equivalent to 231 cubic inches. It is divided into:

• 4 quarts (abbreviation: qt) or
• 8 pints (abbreviation: pt) or
• 32 gills (abbreviation: gi) or
• 128 fluid ounces (abbreviation: fl oz)

• The U.S. dry gallon is equal to 4.404884 litres which is equivalent to 268.8025 cubic inches. It is divided into:

• 4 quarts (abbreviation: dry qt)
• 8 pints (abbreviation: dry pt)

• The Imperial gallon is 20 % larger than the U.S. liquid gallon and is equal to 4.546092 litres which is equivalent to 277.4196 cubic inches. It is divided into:

• 4 quarts (liquid or dry) or
• 8 pints (liquid or dry) or
• 32 gills (liquid or dry) or
• 160 fluid ounces (liquid only) which is about 4% smaller than the fluid ounces in a U.S. gallon

History

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

• The ale gallon, used for measuring beer was defined in England, during the reign (1558 – 1603) of Queen Elizabeth I, as having 282 cubic inches (≈ 4.62115 L).

• The Winchester gallon, or corn gallon, used for measuring dry materials was defined by England's Parliament in 1696 as one-eighth of a Winchester bushel having a volume of a cylinder 18.5 inches in diameter and 8 inches deep. Thus, the Winchester gallon was approximately 268.80252 cubic inches (≈ 4.40488 L).

• The wine gallon, or Queen Anne's gallon, used for measuring wine was defined in England, in 1706 during the reign of Queen Anne, as having a volume of 231 cubic inches (≈ 3.78541 L).

After the American colonies revolted and became independent of the British Empire in 1776, the United States subsequently adopted the Queen Anne gallon of 231 cubic inches (≈ 3.78541 L) for measuring liquids which is now known as the U.S. liquid gallon. The United States also adopted the Winchester gallon of 268.80252 cubic inches (≈ 4.40488 L) for measuring dry materials and it is now known as the U.S. dry gallon.

England made a different decision and, in 1824, the British defined the Imperial gallon as the volume of 10 pounds of water at 62 °F and essentially atmospheric pressure (30 inches of mercury), and chose to use it for measuring both liquids and dry materials. That gave the Imperial gallon a volume of 277.42 cubic inches (4.54610 L) which is approximately 20 percent larger than the U.S. liquid gallon.

Usage

Countries using the U.S. liquid gallon

As of 2005, the U.S. liquid gallon continued to be used as a unit of measure for fuel in Colombia, Dominican Republic, Ecuador, El Salvador, Guatemala, Haiti, Honduras, Liberia, Nicaragua, Panama, Peru, and the United States.

Countries using the Imperial gallon

As of 2000, the Imperial gallon ceased to be a legal unit of measure within the United Kingdom for economic, health, safety or administrative purposes. However, as noted in the introduction (see above), the Imperial gallon is still in unofficial use within the United Kingdom and Ireland and in semi-official use within Canada.