Gas Mileage Calculator
US mpg, imperial mpg, km/L and L/100km, converted properly.
Work out Gas Mileage. US mpg, imperial mpg, km/L and L/100km, converted properly. Free, with no account and nothing to download.
US miles per gallon
30
36.028 imperial mpg · 7.84 L/100km
The US and imperial gallons are genuinely different sizes — 3.785 litres against 4.546 — so the same car reads about 20% better in imperial mpg than in US mpg. That is a unit difference, not a disagreement about the car, and it is the single largest source of confusion in fuel figures. Litres per 100 km inverts the scale: lower is better, and it is the reciprocal of distance per unit fuel rather than a rescaling of it.
How the Gas Mileage Calculator works
The US and imperial gallons are genuinely different sizes — 3.785 litres against 4.546 — so the same car reads about 20% better in imperial mpg. That is a unit difference rather than a disagreement about the car, and it is the largest source of confusion in fuel figures.
Also known as: mpg calculator · mpg to l 100km converter · fuel economy converter · us mpg vs imperial mpg
Two different gallons
The US gallon is 3.785411784 litres and the imperial gallon is 4.54609 — both exact by definition, and about 20% apart.
So the same car reads roughly 20% better in imperial mpg than in US mpg. A 30 mpg US car is a 36 mpg imperial car. Neither figure is wrong; they measure against different gallons.
An inverted scale
Miles per gallon and kilometres per litre measure distance per fuel, so higher is better. Litres per 100 km measures fuel per distance, so lower is better.
They are reciprocals, not rescalings, and that has a consequence people miss: equal steps in mpg are not equal savings. Going from 10 to 15 mpg saves far more fuel over the same distance than going from 30 to 35, even though both are a five-unit improvement.
This is the argument for the L/100km convention — it is linear in the thing that actually costs money.
Frequently asked questions
How do I convert mpg to L/100km?
Divide 235.215 by US mpg, or 282.481 by imperial mpg. 30 US mpg is 7.84 L/100km.
Why is imperial mpg higher than US mpg?
Because an imperial gallon is 4.546 litres against the US gallon's 3.785 — about 20% larger. The same car travels further on the larger gallon.
Is a higher number always better?
For mpg and km/L, yes. For L/100km the scale inverts — lower is better, because it measures fuel consumed rather than distance covered.
Why do real-world figures fall short of official ones?
Official tests use standardised cycles that are gentler than most driving. Cold starts, short trips, high speeds and air conditioning all reduce economy substantially.
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