Fuel Economy Converter
Converts fuel economy between every common unit, including the two different gallons. Because miles per gallon and litres per 100 km are reciprocals, this is the one conversion where doubling the input does not double the answer.
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The formula
L/100 km = 100 ÷ (km per litre)
Distance-per-fuel units (mpg, km/L) and fuel-per-distance units (L/100 km) are reciprocals of one another, so converting between the families means dividing rather than multiplying. That is also why the scales run in opposite directions.
What to watch out for
Two things catch people out:
- The scales run in opposite directions. 50 mpg is better than 40 mpg, but 5 L/100 km is better than 6 L/100 km. Converting flips which end of the scale is good.
- There are two gallons. An imperial gallon is 4.546 litres against the US gallon's 3.785, so a car rated 40 mpg in the UK is only 33.3 mpg in US terms — the same car, a 20% difference in the number.
This is also why savings are not linear. Going from 15 to 20 mpg saves more fuel over the same distance than going from 40 to 50 mpg, even though the second looks like the bigger improvement.
Frequently Asked Questions
What is 30 mpg in litres per 100 km?
7.84 L/100 km using US gallons, or 9.42 L/100 km using imperial gallons.
Why are US and UK mpg different?
They use different gallons. The imperial gallon is 4.54609 litres; the US gallon is 3.785411784 litres. Imperial mpg figures are always about 20% higher for the same car.
Why does Europe use L/100 km instead of mpg?
Fuel per distance answers the question people actually have — how much fuel a journey will need — and it scales linearly, so the saving between two cars is easy to compare. With mpg the same difference means far more at the low end than the high end.
Is a higher or lower number better?
Higher for mpg and km/L; lower for L/100 km. The calculator says which way round the units you picked run.