Gallon

A unit of volume used chiefly in the United States and the United Kingdom. Its size differs between systems, and US customary measures distinguish liquid and dry gallons.

US liquid gallon: A US customary volume unit equal to 231 cubic inches, or exactly 3.785411784 liters. This is the liquid gallon most commonly meant in the United States.
Wine gallon: A historical English volume unit associated with measuring wine and later used as the basis for the US liquid gallon. Its standardized volume underlies the modern US liquid gallon.
Fuel economy in automobiles: A measure of how far a vehicle travels per unit of fuel consumed. Miles per gallon depends on whether the gallon is US or Imperial.
Cubic foot: A volume unit equal to the volume of a cube one foot on each side. It offers a larger geometric unit for comparing gallon-sized volumes.
US dry gallon: A US customary unit of dry volume equal to 268.8025 cubic inches, or about 4.405 liters. The United States also has a larger gallon for dry commodities.
Winchester measure: A historical English system of volume measurement used especially for grain and other dry goods. Its bushel standard is the basis for the US dry gallon.
Milk: A nutrient-rich liquid produced by mammals and commonly sold as a measured commodity. Milk containers in the United States commonly use gallon-sized quantities.
Cubic inch: A volume unit equal to the space inside a cube one inch on each side. The US liquid gallon is legally defined as 231 cubic inches.
Imperial gallon: A British Imperial volume unit equal to exactly 4.54609 liters. This standard defines the gallon used in the United Kingdom and some other countries.
Weights and Measures Act 1824: A British law that established the Imperial system of weights and measures, including the Imperial gallon. The act fixed the British gallon at a distinct volume.

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