Gallon Gallon The gallon () is a unit of measurement for volume and fluid capacity in both the US customary units and the British imperial systems of measurement. Three significantly different sizes are in current use: the imperial gallon defined as litres (4 imperial quarts or 8 imperial pints), which is used in the United Kingdom, Canada, and some Caribbean nations; the US gallon defined as 231 cubic inches (4 US liquid quarts or 8 US liquid pints) or about , which is used in the US and some Latin American and Caribbean countries; and the least-used US dry gallon defined
Gallon one time defined as the volume of a cylinder 6 inches deep and 7 inches in diameter, i.e. . It had been redefined during the reign of Queen Anne, in 1706, as 231 cubic inches exactly, which is the result of the earlier definition with π approximated to . 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 was actually in use, so this statute became necessary. It remains the US definition today. In 1824, Britain adopted a close approximation to the