The gallon is a unit of volume in British imperial units and United States customary units. Three different versions are in current use:the imperial gallon, defined as 4.54609 litres, which is or was used in the United Kingdom, Ireland, Canada, Australia, New Zealand, and some Caribbean countries;
the US gallon, defined as 231 cubic inches, which is used in the United States and some Latin American and Caribbean countries; and
the US dry gallon ("usdrygal"), defined as 1⁄8 US bushel.
A one-US-gallon gas can showing "U.S. Gallon" marking (for American use), imperial gallons (for British use), and litres (for Canadian use)
A Shell petrol station selling 2* and 4* (leaded petrol) by the gallon in the UK, circa 1980
A fuel station in the United States displaying fuel prices per US gallon
An American milk bottle with a volume of one US gallon
The imperial system of units, imperial system or imperial units is the system of units first defined in the British Weights and Measures Act 1824 and continued to be developed through a series of Weights and Measures Acts and amendments.
The former Weights and Measures office in Seven Sisters, London (590 Seven Sisters Road)
Imperial standards of length 1876 in Trafalgar Square, London
A baby bottle that measures in three measurement systems—metric, imperial (UK), and US customary
A one US gallon gas can purchased near the US-Canada border showing equivalences in imperial gallons and litres
