Miles per gallon US (mpg) measures how many miles a vehicle can travel on one US gallon (3.785 liters) of fuel, the standard efficiency metric in the United States. US EPA fuel economy ratings display city and highway mpg figures for every new vehicle. One US mpg equals approximately 0.425 km/L or about 23.52 L/100km.

Miles per gallon UK (imperial mpg) measures distance per imperial gallon (4.546 liters), used in the United Kingdom for fuel economy ratings. Because the imperial gallon is larger than the US gallon, the same car shows a higher mpg figure in the UK system. One UK mpg equals approximately 0.354 km/L or about 28.25 L/100km.