Fuel economy converter
mpg (US) to L/100 km — convert US miles per gallon to litres per 100 km
1 mpg (US) → 235.214583 L/100 km
Convert mpg and litres per 100 km. The relationship is inverse, not a multiplier — a car twice as efficient uses half the fuel.
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mpg (US) to L/100 km
L/100 km to mpg (US)
mpg (UK) to L/100 km
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Read the fuel economy unit guide — what each one is, where it came from, and which of them are quietly different from each other.
Questions
Why can't I convert mpg with a simple multiplier?
Because the two measures run in opposite directions. Miles per gallon counts distance per unit of fuel; litres per 100 km counts fuel per unit of distance. One is the reciprocal of the other, so you divide rather than multiply.
Why is UK mpg always a bigger number than US mpg?
The Imperial gallon is about 20% larger, so the same car travels further on one of them. A car rated 30 mpg in the US is around 36 mpg in the UK, with nothing about the car having changed.
Going from 15 to 20 mpg, or 30 to 40 mpg — which saves more fuel?
The first, by a wide margin. Over 10,000 miles the 15-to-20 change saves about 167 gallons; the 30-to-40 change saves about 83. This is exactly the trap the inverse relationship sets, and why litres per 100 km is the easier measure to reason with.
All fuel economy units and their conversion factors
| Unit | Symbol | In litres per 100 km |
|---|---|---|
| Litres per 100 km | L/100 km | 1 |
| US miles per gallon | mpg (US) | 235.214583 ÷ value |
| Imperial miles per gallon | mpg (UK) | 282.480936 ÷ value |
| Kilometres per litre | km/L | 100 ÷ value |
| Miles per litre | mi/L | 62.137119 ÷ value |