How to Convert MPG and Litres per 100 Kilometres

Identify which gallon a quoted MPG figure uses before comparing vehicles.

Use the Fuel Economy Converter alongside this illustrative example.

A practical example

A vehicle consuming 8 L/100 km travels 12.5 km on a litre. That corresponds to about 29.4 MPG with US gallons and 35.3 MPG with imperial gallons. The vehicle has not become more efficient; the gallon has changed.

Check the result

Write the gallon convention beside every MPG figure. For L/100 km, a smaller number means lower fuel use; for km/L or MPG, a larger number means more distance from the same fuel.

Try a comparison

Compare 8 and 10 L/100 km directly. The latter uses two additional litres per hundred kilometres, or 25% more fuel over the same distance. MPG moves in the opposite direction because its distance-per-fuel relationship is reciprocal.

What this does not establish

Conversion standardises units, not test conditions. City and highway figures, driving style and load can still make two published numbers unsuitable for direct comparison.

Report unclear guidance or a result that needs checking.