Fuel Efficiency Converter
mpg, L/100km, and the 20% gallon problem.
Convert Fuel Efficiency. mpg, L/100km, and the 20% gallon problem. Refuses out-of-range input instead of guessing.
Optional — gives running cost.
Fuel consumption
7.84 L/100km
30 US mpg · 36 imperial mpg
The US and imperial gallons differ by about 20% — 3.785 litres against 4.546 — so an unlabelled mpg figure is ambiguous by a fifth. That gap is larger than most of the differences people agonise over when comparing cars. mpg and L/100km run in opposite directions and the relationship is reciprocal, not linear. Going from 15 to 20 mpg saves far more fuel over the same distance than going from 40 to 50, even though the second improvement looks bigger. That is why L/100km is the better unit for comparing savings. Published figures come from standardised test cycles. Real-world consumption is commonly 10-20% worse, and short cold journeys can be far worse again.
How the Fuel Efficiency Converter works
Convert between US mpg, imperial mpg, litres per 100 km and kilometres per litre, with running cost if you add a fuel price. The two gallons differ by about 20%, which makes an unlabelled mpg figure ambiguous by a fifth.
Also known as: mpg to l/100km converter · us mpg to imperial mpg · fuel consumption converter · km per litre calculator
Frequently asked questions
What is the difference between US and imperial mpg?
The gallon. A US gallon is 3.785 litres and an imperial gallon is 4.546, so the same car scores about 20% higher in imperial mpg. An unlabelled figure is ambiguous by more than most car-to-car differences.
How do I convert mpg to L/100km?
Divide 235.2 by US mpg, or 282.5 by imperial mpg. The relationship is reciprocal rather than linear, which is why the two scales run in opposite directions.
Why is L/100km better for comparing savings?
Because fuel saved is not linear in mpg. Going from 15 to 20 mpg saves far more fuel over the same distance than going from 40 to 50, even though the second improvement looks larger. L/100km makes that obvious.
Why is my real economy worse than the published figure?
Published figures come from standardised test cycles under ideal conditions. Real-world consumption is commonly 10-20% worse, and short cold journeys can be far worse again because the engine never reaches efficient temperature.
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