Fuel Economy Converter (MPG to L/100 km)
Convert mpg to L/100 km, km per litre and UK mpg, and back.
Good to know. Going from 10 to 20 mpg saves more fuel than going from 30 to 50. L/100 km shows it; mpg hides it.
How it works
In plain words
Miles per gallon and litres per 100 km measure opposite things: distance per fuel, and fuel per distance. So each one is a fixed number divided by the other. For US gallons that number is 235.215; for the larger UK gallon it is 282.481; km per litre is 100 divided by L/100 km.
The formula
L/100 km = 235.215 ÷ mpg (US) L/100 km = 282.481 ÷ mpg (UK) L/100 km = 100 ÷ km/L mpg (UK) = mpg (US) × 1.20095
Worked example
A car using 7 L/100 km: 235.215 ÷ 7 = 33.6 mpg in US gallons, or 40.35 mpg in UK gallons.
Sources
- NIST Special Publication 811, Guide for the Use of the International System of Units, Appendix B Exact conversion factors for US customary units.
- Weights and Measures Act 1985, Schedule 1 1 UK gallon = 4.54609 litres.
Sources checked September 29, 2026. 7 automated tests check its answers on every change.
About the fuel economy converter (MPG to L/100 km)
Most of the world measures fuel economy as litres per 100 km: how much fuel a distance takes, so lower is better. The US and the UK use miles per gallon, how far a gallon goes, so higher is better. Some countries, including Japan and India, use kilometres per litre.
Because one is the upside-down of the other, the conversion is a division. 235.215 divided by US mpg gives L/100 km, and the same division goes back. The UK gallon is about 20% larger than the US one, so the same car has a higher mpg figure in the UK: 30 US mpg is 36 UK mpg.
The upside-down scale also makes mpg misleading. Improving a car from 10 to 20 mpg halves its fuel use, saving 5 gallons every 100 miles. Going from 30 to 50 mpg saves only 1.3 gallons over the same distance. Fuel per distance shows savings as they are, which is why the US window sticker now shows gallons per 100 miles too.
Official figures come from test cycles and are often better than real driving. The European WLTP and the US EPA cycles differ, so compare cars on the same test.
Questions people ask
How do I convert mpg to L/100 km?
Divide 235.215 by US mpg, or 282.481 by UK mpg. 30 US mpg is 7.84 L/100 km.
How do I convert L/100 km to mpg?
Divide 235.215 by the L/100 km for US mpg. 6 L/100 km is 39.2 US mpg, or 47.1 UK mpg.
What is good fuel economy in L/100 km?
For a petrol car, under about 6 L/100 km (39 US mpg) is good today; hybrids reach 4–5 L/100 km.
Why are UK mpg figures higher than US ones?
A UK gallon is 4.546 litres and a US gallon 3.785 litres, so a UK gallon takes you about 20% further.