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
Metrication in the United States fl oz, and 24 fl oz (355, 473, 591 and 710 mL) sizes. The half-liter water bottle (16.9 fl oz) has nearly replaced the 16 ounce size. 700 mL (23.6 fl oz) and one-liter sizes are also common, though 20 fl oz, and 24 fl oz sizes remain popular, particularly in vending machines. Attempts to sell 3- or 4-liter jugs of milk, instead of gallons (3.785 L), have been largely unsuccessful, and such bottles are rarely seen in the United States. Milk remains sold in binary divisions of the gallon, with half-pints, pints, quarts and half-gallons being the primary sizes.