Fuel Economy Converter
Convert mpg (US and UK), L/100 km, and km per liter.
What is Fuel Economy?
Fuel economy measures distance per volume (mpg, km/L) while most of the world quotes consumption, volume per distance (L/100 km). The two are reciprocals rather than multiples, so a higher mpg is better while a higher L/100 km is worse — the direction flips, which is where the confusion comes from.
How it works
Both families pass through a common measure, kilometres per litre, and the inverse step is applied for L/100 km (100 ÷ L/100 km). The US gallon (3.785411784 L) and the imperial gallon (4.54609 L) have separate factors, because the same mpg number means different economy in the two countries.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
US mpg to L/100 km
Enter 30 mpg and read 7.84 L/100 km — the figure a European car's consumption would be quoted as.
Common mistakes
US mpg vs imperial mpg
An imperial gallon is about 20% larger, so the same car reads roughly 20% higher mpg in the UK than in the US. Pick the gallon that matches the figure's source.
Reading L/100 km backwards
Lower is more efficient. Comparing L/100 km as if it were mpg reverses the ranking, which is why the result note states the direction.
Frequently asked questions
Why is there no simple multiply factor?
Because L/100 km and mpg are inverse measures. A fixed factor only exists between mpg (US), mpg (UK), km/L and mi/L; L/100 km requires the reciprocal step this converter applies.
Which gallon does mpg use?
US mpg uses the US gallon and imperial mpg the UK gallon. The converter keeps them as separate units so the two are never mixed.