Reading fuel economy in mpg from an overseas car review doesn't translate intuitively to km/L or L/100km — and to make it worse, US mpg and UK mpg aren't the same either.
US mpg vs UK mpg — same number, different meaning
US mpg is based on the US gallon (3.785L); UK mpg is based on the UK gallon (4.546L). The same "30 mpg" actually represents worse fuel economy in UK mpg, so always check which country's figure you're looking at.
For L/100km, lower is better
km/L and mpg both work so that a bigger number means better economy — but L/100km (liters needed to travel 100km) works the opposite way: a smaller number is better. Mixing this up when reading a European spec sheet flips the interpretation entirely.
Rated economy vs. real-world economy
A manufacturer's rated fuel economy (mpg, km/L) is measured under standardized test conditions, so real city driving or running the AC often comes in below the official figure — worth keeping in mind.
Conversion formulas
| Conversion | Formula |
|---|---|
| mpg (US) → km/L | mpg × 0.4251 |
| mpg (UK) → km/L | mpg × 0.3540 |
| km/L → L/100km | 100 ÷ km/L |
Try it now
FastestUnitConverter's fuel economy converter handles US/UK mpg, km/L, and L/100km all at once.
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