Fuel economy converter
Enter a fuel economy figure and choose the unit it is in. You get the same figure in the unit you want, and in all four units. L/100 km is a reverse scale, so it cannot be converted by multiplying.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Type the figure. A dot or a comma works as the decimal separator.
- Choose the unit it is in and the unit you want.
- The result and all four units are shown below the form.
How it works
All four units describe the same thing, so the tool first converts your figure to litres per 100 km, then to the unit you chose.
- km/L = 100 / (L/100 km)
- mpg (US) = 100 × 3.785411784 / (1.609344 × L/100 km) = 235.2146 / (L/100 km)
- mpg (UK) = 100 × 4.54609 / (1.609344 × L/100 km) = 282.4809 / (L/100 km)
A mile is 1.609344 km exactly. The same constants work in both directions.
Worked example
A car that uses 6.5 L/100 km does 100 / 6.5 = 15.38 km/L, 235.2146 / 6.5 = 36.19 mpg (US) and 282.4809 / 6.5 = 43.46 mpg (UK).
Common mistakes
- Using the US gallon figure for a UK car or the reverse: the two gallons differ by about 20%.
- Averaging mpg across trips. Average the L/100 km instead, because fuel use adds up per distance, not per mile per gallon.
Frequently asked questions
How do I convert L/100 km to mpg?
Divide a constant by the figure. For US gallons, mpg = 235.2146 / (L/100 km); for imperial gallons, mpg = 282.4809 / (L/100 km). So 8 L/100 km is 29.40 mpg (US) or 35.31 mpg (UK).
Why is this not a simple unit converter?
L/100 km measures fuel used per distance, while mpg and km/L measure distance per fuel. Doubling one halves the other, so the conversion is a reciprocal and the normal multiply-by-a-factor method does not work.
Why is a UK mpg bigger than a US mpg?
An imperial gallon is 4.54609 litres, a US gallon 3.785411784 litres, so the same car covers about 20% more miles per imperial gallon. 30 mpg (US) is about 36 mpg (UK).
Which is better, a high L/100 km or a high mpg?
Opposite ways round. Lower L/100 km means a more economical car, higher mpg or km/L does too. 5 L/100 km is 47.04 mpg (US) and 20 km/L.
Why does the tool ask for a value above zero?
A value of zero in L/100 km would be a car using no fuel, and zero in mpg or km/L would need an infinite amount. Neither can be converted.