Miles per Gallon (UK) to Miles per Gallon (US) Converter | mpg (UK) to mpg (US)

What this converter does

If you are used to UK miles per gallon and you come across an American figure, the numbers will not line up, because the two countries measure the gallon differently. This converter takes a UK mpg figure and gives you the US equivalent. Enter the UK value and read off the US one, so a British economy figure makes sense in American terms.

The conversion factor

The conversion is a single multiplication:

mpg (US) = mpg (UK) × 0.832674

That factor is just the ratio of the gallons the other way round, and it is the exact inverse of the US-to-UK figure. Every UK mpg value comes out lower when expressed in US mpg, by about 17 percent.

Why the US figure comes out lower

A UK gallon, the Imperial one, is about 4.546 litres, while a US gallon is about 3.785 litres, so the UK gallon is the larger of the two. When you switch to the smaller US gallon, a car covers fewer miles on it, so the mpg figure drops. The car has not changed and is no thirstier than it was; it is simply being measured against a smaller gallon. This is why British cars, which often boast high mpg figures, look markedly less economical the moment their numbers are put into US terms.

A worked example

Say a British car is rated at 50 mpg and you want to know what that is in US mpg.

• 50 × 0.832674 = 41.6 mpg (US)

So a 50 mpg UK car is about 41.6 mpg in the US. That is still respectable, but it is a fair bit short of the 50 the UK figure suggested, which is exactly the gap the smaller US gallon opens up. Converting keeps you from over-estimating a car's economy when reading across the two systems.

Common mpg (UK) values in mpg (US)

As anchors, 40 mpg UK is about 33.3 mpg US, and a strong 60 mpg UK comes out near 50 mpg US.

Where you will need it

This is the conversion for a UK reader making sense of American figures. US car reviews, manufacturer ratings, and forums all quote economy in US mpg, so converting your own UK frame of reference lets you read them without being misled. It comes up when researching a model sold in both markets, when looking at an American import, or any time a US mpg figure has to be judged against the UK numbers you already know. The American figure will always look lower, and this tells you how much of that is the gallon rather than the car.

Questions people ask

How do I convert UK mpg to US mpg?

Multiply the UK mpg figure by 0.832674. The US figure is lower because the US gallon is about 17 percent smaller than the UK gallon.

Why does the same car score lower in US mpg?

The US gallon is smaller, so a car travels fewer miles on one. The same car therefore scores a lower mpg in US terms, even though it is no thirstier.

What is 50 UK mpg in US mpg?

About 41.6 mpg. It is a handy anchor for remembering how much UK figures shrink in US terms.

References

1. National Institute of Standards and Technology (NIST), Special Publication 811, Guide for the Use of the International System of Units (gallon definitions and unit conversions). https://www.nist.gov/pml/special-publication-811
2. U.S. Department of Energy and EPA, fueleconomy.gov (fuel economy ratings and information). https://www.fueleconomy.gov/