The British imperial gallon is now defined as exactly 4.54609 litres (277.4194 cubic inches).
It is used in some Commonwealth countries.
Until 1976 it was based on the volume of 10 pounds (4.5359 kg) of water at 62 °F (17 °C).
There are four quarts in a gallon, the imperial pint is defined as 0.56826125 litres (i.e.  gallon) and there are 20 imperial fluid ounces in an imperial pint.
The British imperial gallon is now defined as exactly 4.54609 litres (277.4194 cubic inches). It is used in some Commonwealth countries. Until 1976 it was based on the volume of 10 pounds (4.5359 kg) of water at 62 °F (17 °C). There are four quarts in a gallon, the imperial pint is defined as 0.56826125 litres (i.e.  gallon) and there are 20 imperial fluid ounces in an imperial pint.
Gallon