Fuel Economy Converter
Convert fuel economy between US mpg, UK mpg, liters per 100 km and kilometers per liter.
Why mpg and L/100 km work in opposite directions
Miles per gallon measures distance per unit of fuel, so higher is better. Liters per 100 km measures fuel per unit of distance, so lower is better. Because one is the reciprocal of the other, you cannot convert with a simple multiplier.
L/100 km = 235.215 ÷ US mpg L/100 km = 282.481 ÷ UK mpg
A car rated at 30 mpg (US) uses 235.215 ÷ 30 = 7.84 L/100 km.
US vs UK mpg
A UK (imperial) gallon is about 20% larger than a US gallon, so the same car shows about 20% higher mpg in the UK. 30 US mpg equals 36 UK mpg.
The mpg illusion
Going from 10 to 20 mpg saves more fuel than going from 30 to 50 mpg over the same distance. L/100 km makes this obvious: 23.5 → 11.8 L/100 km versus 7.8 → 4.7 L/100 km. That is why many economists prefer fuel-per-distance measures.
Frequently asked questions
How do I convert mpg to L/100km?
Divide 235.215 by the US mpg figure. 25 mpg is about 9.4 L/100 km.
What is a good L/100km?
Under about 6 L/100 km is very efficient for a petrol car; 8–10 is typical for midsize cars and SUVs.
Why does my car show higher mpg in the UK?
UK mpg uses the larger imperial gallon, so the number is about 20% higher for the same fuel use.
Last reviewed October 2026. Results are estimates; check important decisions with a qualified professional.