imp gal
Imperial Gallon
The imperial gallon is a unit of volume equal to 4.546 liters, used in the United Kingdom and some Commonwealth countries. It is approximately 20% larger than the US gallon (3.785 liters).
History
The imperial gallon was defined by the British Weights and Measures Act of 1824 as the volume of 10 pounds of water at 62°F. It replaced several older gallon measures. While the UK has largely metricated, the imperial gallon is still used for fuel economy ratings in some countries.