Fuel Economy & EV Efficiency Converter

Why does L/100km go down when a car gets more efficient?

Most efficiency units work the intuitive way — higher is better. A car doing 20 km/L is more efficient than one doing 10 km/L, just as 40 mpg beats 20 mpg. But L/100km measures consumption, not efficiency: it tells you how many litres the car burns to travel 100 km. Less fuel = smaller number = better car. This makes L/100km the exact inverse of km/L, and the two are always related by: km/L = 100 ÷ L/100km.

Bar length = litres burned per 100 km. The efficient car burns one-third of what the thirsty car does, so its bar is one-third as wide — even though it is three times as efficient in km/L terms.

US gallon vs UK (imperial) gallon — never mix them up

MPG figures are not interchangeable between the US and UK. One US gallon is 3.785 L; one imperial gallon is 4.546 L — about 20% larger. The same car always shows a higher mpg figure in the UK than the US. A claim of "33 mpg" means something very different depending on which gallon is being used, so always check.

Petrol / Diesel reference table

Common fuel economy values in all four units. The highlighted row is a typical mid-size petrol car.

Electric vehicle (EV) reference table

Common EV efficiency values in all five units. The highlighted row is a typical mainstream EV. kWh/100km and Wh/km are lower-is-better; the other three are higher-is-better.