Fuel Economy converter

Fuel economy can be expressed in two opposite ways. Distance-per-volume units, such as miles per gallon (mpg) or kilometers per liter, tell how far a vehicle travels on a given amount of fuel, so higher is better. Liters per 100 kilometers, used across Europe and much of the world, tells how much fuel is needed to cover a fixed distance, so lower is better.

Convert between 6 fuel economy units. Pick any two units below; results update as you type.

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Popular fuel economy conversions

About fuel economy units

Because mpg and L/100 km are reciprocals, converting between them means dividing into a constant rather than multiplying. Miles per gallon also differs by country: the US gallon is smaller than the imperial gallon, so the same car shows a higher mpg figure in the UK than in the US, by about 20%.

Consumption units such as L/100 km make fuel savings easier to compare, since cutting consumption from 10 to 8 L/100 km saves exactly the same fuel as cutting from 8 to 6 over the same distance.

Tips

Improving a low-mpg vehicle saves more fuel than the same mpg gain on an efficient one, because fuel use follows the reciprocal.
Check whether a mpg figure uses US or UK gallons before comparing vehicles from different markets.
For L/100 km, a smaller number means better efficiency, the opposite of mpg and km/L.

All fuel economy units

Unit	Symbol
Kilometers per Liter	km/L
Miles per Liter	mi/L
Kilometers per US Gallon	km/gal
Miles per US Gallon	mpg
Miles per Imperial Gallon	mpg (UK)
Liters per 100 km	L/100 km

Factors: NIST SP 811 · SI Brochure · NIST Handbook 44 — Updated October 17, 2026