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 in fuel economy expression in Canada and the United Kingdom are imperial gallons. Despite its status as a U.S. territory, and unlike American Samoa, the Northern Mariana Islands, Guam, and the U.S. Virgin Islands, Puerto Rico ceased selling gasoline by the US gallon in 1980. The gallon was removed from the list of legally defined primary units of measure catalogued in the EU directive 80/181/EEC for trading and official purposes, with effect from 31 December 1994. Under the directive the gallon could still be used – but only as a supplementary or secondary unit. One of the effects of this