How this calculator works
Distance and fuel must describe the same interval, such as two full-tank refills where the second fill returns the tank to full. Dividing fuel by distance gives consumption per kilometre, scaled to 100 kilometres for the Canadian convention. The mile-per-gallon figures use exact unit definitions: 1.609344 km per mile, 3.785411784 litres per US gallon and 4.54609 litres per Imperial gallon.
Formula
litres_per_100km = 100 x fuel_litres / distance_km. km_per_litre = distance_km / fuel_litres. mpg_us = (distance_km / 1.609344) / (fuel_litres / 3.785411784). mpg_imperial = (distance_km / 1.609344) / (fuel_litres / 4.54609).
Worked example
600 km on 45 litres is 7.5 L/100 km, 13.333333 km/L, 31.361944 US mpg and 37.664125 Imperial mpg. Zero distance or zero fuel is rejected because the economy figures would be undefined.
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Frequently asked questions
Which mpg figure should I use?
Use US mpg for the United States and Imperial mpg for the United Kingdom and older Canadian references. The two gallons differ by about 20 percent, so the numbers are not interchangeable.
Why are both distance and fuel required to be above zero?
This page returns both consumption and economy, and each is the other inverted. A zero in either input would make at least one of the answers undefined.
How do I measure fuel accurately?
Fill the tank, record the odometer, drive normally, then refill at the same pump to the same full point. The litres added at the second fill are the fuel used over the recorded distance.