The US gallon (gal) is an imperial volume unit equal to exactly 3.7854 liters, the standard measurement for fuel, milk, and paint in the United States. Gasoline prices at American pumps are always quoted per gallon, and US vehicle fuel efficiency is measured in miles per gallon. One US gallon equals 4 US quarts or 8 US pints.

The UK gallon (imperial gallon) equals exactly 4.54609 liters, about 20% larger than the US gallon, and remains the standard fuel measurement in the United Kingdom and some Commonwealth nations. British fuel efficiency is expressed in miles per imperial gallon, which yields higher numbers than the US equivalent. One UK gallon equals approximately 1.201 US gallons.