There were a number of systems of liquid measurements in the United Kingdom prior to the 19th century.

[4] It is used in some Commonwealth countries, and until 1976 was defined as the volume of water at 62 °F (16.67 °C)[5][6] whose mass is 10 pounds (4.5359237 kg).

In order to overcome the effects of expansion and contraction with temperature when using a gallon to specify a quantity of material for purposes of trade, it is common to define the temperature at which the material will occupy the specified volume.

For example, the volume of petroleum products[9] and alcoholic beverages[10] are both referenced to 60 °F (15.6 °C) in government regulations.

[12] As of 2021, the imperial gallon continues to be used as the standard petrol unit on 10 Caribbean island groups, consisting of: All 12 of the Caribbean islands use miles per hour for speed limits signage, and drive on the left side of the road.

The United Arab Emirates ceased selling petrol by the imperial gallon in 2010 and switched to the litre, with Guyana following suit in 2013.

[30][19] In the European Union the gallon was removed from the list of legally defined primary units of measure catalogue in the EU directive 80/181/EEC for trading and official purposes, effective from 31 December 1994.

[31] As a result of the EU directive Ireland and the United Kingdom passed legislation to replace the gallon with the litre as a primary unit of measure in trade and in the conduct of public business, effective from 31 December 1993, and 30 September 1995 respectively.

However, barrels and large containers of beer, oil and other fluids are commonly measured in multiples of an imperial gallon.

Thus, both gallons are equal to four quarts, eight pints, sixteen cups, or thirty-two gills.

This suggests a common origin in Romance Latin, but the ultimate source of the word is unknown.

[53] The gallon originated as the base of systems for measuring wine and beer in England.

It was redefined during the reign of Queen Anne, in 1706, as being exactly 231 cubic inches, the earlier definition with π being approximated as ⁠22/7⁠.

Inspired by the kilogram-litre relationship[citation needed], the imperial gallon was based on the volume of 10 pounds of distilled water weighed in air with brass weights with the barometer standing at 30 inches of mercury (100 kilopascals; 15 pounds per square inch) and at a temperature of 62 °F (17 °C).