Liters per 100km (L/100km) is the inverse fuel efficiency metric used in Europe and Australia, measuring how many liters of fuel a vehicle consumes over 100 kilometers. Lower numbers mean better efficiency — a car rated at 5 L/100km uses less fuel than one rated at 8 L/100km. This is the inverse of km/L: L/100km = 100 / km/L.

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.