Fuel Economy Converter
Convert between US MPG, imperial MPG, L/100 km, and km/L — the non-linear maths handled for you.
- mpg
- fuel economy
- l/100km
- km/l
- gas
- mileage
- imperial gallon
- us gallon
About Fuel Economy Converter
Fuel economy is measured in different units depending on where you are. The US and UK quote miles per gallon (MPG), but their gallons are different sizes — a US gallon is 3.785 L, an imperial (UK) gallon is 4.546 L — so the same car gets different MPG ratings on either side of the Atlantic. Canada, Europe, and most of the world use L/100 km instead, which is the inverse: how much fuel to cover a fixed distance, where lower is better. A handful of countries also use km/L.
The conversion is non-linear because MPG and L/100 km are reciprocals of each other (efficiency vs consumption). This converter normalises everything through km/L internally and converts cleanly between all four units.
How to use
Type a value and pick which unit it's in. The other three units update instantly with the equivalent figure. Click any result to copy it.
Quick reference points: 30 mpg (US) is about 7.8 L/100 km. 50 mpg (US) is about 4.7 L/100 km — the modern hybrid territory. 20 mpg (US) is around 11.8 L/100 km — typical of older or larger vehicles. The relationship is hyperbolic, so the same gap in MPG doesn't represent the same fuel saving at every level: going from 15 to 20 MPG saves more fuel per kilometre than going from 35 to 40 MPG.
Frequently asked questions
Why are US and UK MPG different?
Because the gallon is a different size in each country. A US gallon is 3.785 litres (the old US wine gallon, kept after the metric switch); an imperial gallon (UK, Canada historically) is 4.546 litres. So a car rated at 30 mpg (US) gets ~36 mpg (UK) — same physical efficiency, different gallon. Always check which gallon when comparing MPG figures from different sources, especially online used-car listings that mix UK and US data.
Why does Europe use L/100 km instead of MPG?
Because L/100 km is linear in fuel consumed per kilometre, which is the quantity that scales when you compare two cars on the same trip. MPG is the reciprocal — efficiency, not consumption — and improvements at high MPG are deceptively small. Going from 25 to 30 mpg saves more fuel per 100 km than going from 50 to 60 mpg, even though the MPG gain is "5" in both cases. L/100 km removes that illusion.
Is km/L common anywhere?
Yes — Japan, India, and several South American and African countries use km/L instead of L/100 km. It's essentially MPG in metric units (higher is better). It's the direct reciprocal of L/100 km divided by 100: 10 km/L = 10 L/100 km, 20 km/L = 5 L/100 km, and so on.
What's a good MPG / L/100 km for a modern car?
Rough guides (combined city + highway): subcompact petrol cars around 35 mpg US / 6.7 L/100 km. Mid-size sedans around 30 mpg US / 7.8 L/100 km. SUVs around 25 mpg US / 9.4 L/100 km. Modern hybrids 45–55 mpg US / 4.3–5.2 L/100 km. Plug-in hybrids vary wildly depending on how much driving is electric. Pure EVs use MPGe (US) or kWh/100 km (Europe), which this converter doesn't cover.
Do these conversions account for diesel vs petrol?
No — the conversion is purely between units of volume per distance (or vice versa) and doesn't care what fuel is in the tank. A diesel's L/100 km figure converts to the same MPG figure as a petrol car's L/100 km, even though a litre of diesel has more energy and emits more CO₂ per litre than petrol. To compare fuels on energy or emissions you'd need a different calculator entirely.