Gallons

A gallon is a unit of volume used primarily in the United States and several Commonwealth countries. The term has historical roots in medieval England, where various local measures were called a gallon. In modern practice, two main definitions are in active use: the U.S. gallon and the imperial (British) gallon.

The U.S. gallon is defined as 231 cubic inches, which equals 3.785411784 liters. It is the standard for most liquid measures in the United States and is widely used for beverages, fuels, and water.

The imperial gallon, used in the United Kingdom and some Commonwealth nations, is defined as 277.419 cubic inches, equal to 4.54609 liters. It differs from the U.S. gallon by about 20 percent; it remains in use in certain official measurements and historical data.

Dry and related measures: In the United States, there is also a US dry gallon, defined as 268.8025 cubic inches, or 4.40488377 liters, used for dry commodities such as grains. The imperial system historically used different dry measures, but today the gallon is primarily a liquid unit in most contexts.

Conversions: 1 U.S. gallon = 3.785411784 liters; 1 imperial gallon = 4.54609 liters; 1 U.S. dry gallon = 4.40488377 liters. The choice of gallon depends on regional convention and the context of measurement.