MPG UK vs US EPA Explained
Every non-electric vehicle page on this site shows two combined MPG figures: one calculated in UK imperial gallons, one from the US EPA test cycle. They're often noticeably different for the exact same car — here's why, and which one to trust for your own driving.
Two different gallons
A UK (imperial) gallon is about 4.546 litres. A US gallon is smaller, at about 3.785 litres. Because a US gallon holds less fuel, the same real-world fuel consumption produces a higher mpg number when measured in US gallons than in UK gallons — roughly 20% higher, all else being equal. This alone accounts for a meaningful chunk of the gap you'll see between the two figures on this site.
Different test cycles too
On top of the gallon-size difference, the UK/EU and US EPA use different official test procedures to measure fuel economy in the first place — different speed profiles, acceleration rates, and test duration. The US EPA cycle in particular is designed to reflect more realistic city and highway driving, including harder acceleration, which tends to produce lower raw mpg numbers before the gallon-size conversion is even applied.
Which figure should you trust?
Neither figure perfectly predicts your own fuel bill — both are standardised lab tests, not a guarantee of what you'll get with your driving style, load, tyre pressure and local terrain. Use the UK figure if you're comparing cars for UK driving and fuel prices; use the US EPA figure for US driving and prices. This site shows both on every applicable vehicle page specifically so you can compare like-for-like regardless of which market you're shopping in.
Frequently Asked Questions
Why is the US mpg figure usually higher than the UK figure for the same car?
Mainly because a US gallon is about 17% smaller than a UK (imperial) gallon, so the same fuel consumption produces a higher mpg number when expressed in US gallons.
Can I convert directly between UK and US mpg?
Roughly, yes — multiply UK mpg by about 0.83 to estimate the US mpg equivalent, or divide US mpg by about 0.83 to estimate UK mpg — though the different test cycles mean this is an approximation, not an exact conversion.
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