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MPG (US) to MPG (UK)

1 Miles per Gallon (US) (mpg (US)) = 1.20095Miles per Gallon (UK) (mpg (UK))

By KAMP Inc. / UnitOwl · Last reviewed:

Result
1.20095 mpg (UK)
1 mpg (US) = 1.20095 mpg (UK)
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What Is the Difference Between US and UK MPG?

One US mile per gallon equals approximately 1.201 UK (imperial) miles per gallon. To convert US MPG to UK MPG, multiply the US MPG value by 1.201. The difference exists because the US gallon (3.785 liters) is smaller than the imperial gallon (4.546 liters). Since you get more distance from a larger gallon, UK MPG numbers are always about 20% higher than US MPG for the same vehicle. This causes constant confusion when comparing American and British car reviews, buying a used car across borders, or reading fuel economy data from different English-speaking countries. A car rated at 30 US MPG is 36 UK MPG — same car, same efficiency, different number. It is one of the easiest traps in international car shopping because both values are labeled MPG even though the gallon size changed. Converting correctly keeps British reviews, auction listings, and forum posts from looking artificially better to US readers. It also makes cross-border fuel-cost comparisons much fairer. Without that check, imported listings can look better than they are.

How to Convert Miles per Gallon (US) to Miles per Gallon (UK)

  1. Start with your fuel economy in US MPG.
  2. Multiply the US MPG value by 1.201 to get UK MPG.
  3. The result is your fuel economy in imperial miles per gallon.
  4. For a quick estimate, add 20% to the US MPG value. 30 US MPG + 20% = 36 UK MPG (actual: 36.0).
  5. The factor 1.201 comes from the ratio of gallon sizes: 4.546/3.785 = 1.201.

Real-World Examples

An American car review says a sedan gets 35 US MPG. What would the UK rating be?
35 x 1.201 = 42.0 UK MPG. British readers would see this as 42 MPG in their familiar units.
A US truck is rated at 20 MPG. What is that in UK MPG?
20 x 1.201 = 24.0 UK MPG. Still modest by European standards even with the larger gallon.
You are comparing a 40 US MPG hybrid to a UK listing showing 45 UK MPG.
40 x 1.201 = 48.0 UK MPG. Your hybrid is actually more efficient than the UK listing.
A used car advertisement in the UK claims 55 MPG. Is that really 55 US MPG?
No. 55 UK MPG / 1.201 = 45.8 US MPG. Always check which gallon is being used.
A crossover is rated at 28 US MPG on an American listing.
28 x 1.201 = 33.6 UK MPG. That is the number a British review would typically quote for the same vehicle.

Quick Reference

Miles per Gallon (US) (mpg (US))Miles per Gallon (UK) (mpg (UK))
11.20095
22.4019
56.00476
1012.0095
2530.0238
5060.0476
100120.095
500600.476
1,0001200.95

History of Miles per Gallon (US) and Miles per Gallon (UK)

The imperial gallon and US gallon diverged in 1824 when the British Weights and Measures Act redefined the gallon as the volume of 10 pounds of water at 62°F, giving 4.546 liters. The US had already adopted a gallon based on the older English wine gallon of 231 cubic inches (3.785 liters). This 20% difference has caused confusion ever since, particularly in fuel economy comparisons. Canada officially uses L/100km but many Canadians still think in MPG — and they may mean either US or imperial, depending on their age and proximity to the border.

Common Mistakes to Avoid

  • Dividing by 1.201 instead of multiplying. This converts UK MPG to US MPG (the opposite direction). US MPG numbers should always be smaller than UK MPG for the same vehicle.
  • Assuming MPG means the same thing worldwide. An advertisement claiming "50 MPG" could mean 50 US MPG (very efficient) or 50 UK MPG (good but less impressive, equivalent to 41.6 US MPG). Always check which gallon is referenced.
  • Ignoring the difference because "it is only 20%." At 40 MPG, the difference between US and UK gallons means 2.35 vs. 2.82 L/100km of actual fuel savings when comparing two vehicles. Over a year of driving, this translates to hundreds of dollars.
  • Comparing converted UK MPG figures straight against EPA numbers without considering the test cycle. Even after unit conversion, a UK WLTP or older NEDC figure can still look better than a US EPA result for the same car because the underlying test method changed.
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Frequently Asked Questions

Why are there two different gallons?
Historical accident. The US gallon is based on the English wine gallon (231 cubic inches), adopted before independence. The imperial gallon was redefined by Britain in 1824 as 10 pounds of water (277.4 cubic inches). The US never adopted the new British definition.
Which MPG do Canadian cars use?
Canada officially uses L/100km for all vehicle fuel economy labeling since metrication. However, older Canadians may reference imperial MPG, while those near the US border may use US MPG. When a Canadian says "MPG," clarify which gallon they mean.
Does this difference affect fuel prices too?
Fuel is sold by the liter in the UK and Canada, so gallon size does not affect pump prices. In the US, fuel is sold by the US gallon. If comparing price per gallon between the US and a UK equivalent, you would need to account for the gallon difference.
How much larger is an imperial gallon than a US gallon?
An imperial gallon is 4.546 liters, while a US gallon is 3.785 liters. That makes the imperial gallon about 20.1% larger, which is why UK MPG values are about 20% higher for the same vehicle.
Can two identical cars have different US and UK MPG labels but the same real efficiency?
Yes. The underlying vehicle can be identical while the published MPG number changes only because the gallon size changed. That is why it is often clearer to compare both cars in L/100km or km/L if you want to remove the gallon-size confusion.
Quick Tip

The easiest way to remember this conversion: UK MPG is always about 20% higher than US MPG for the same car. If a British car review seems to claim surprisingly good fuel economy, check whether they are using imperial gallons. Multiply by 0.833 (divide by 1.2) to get the approximate US MPG equivalent.

Sources & References