Convert MPG (UK) to MPG (US)
MPG (UK) to MPG (US) is the conversion you need when a car's fuel figure is quoted in imperial (UK) miles per gallon but you want it in the US number. One MPG (UK) is about 0.8326742 MPG (US), so the number always gets smaller when you switch from UK to US — because the UK gallon is bigger than the US one.
Miles per gallon (UK) to Miles per gallon (US) conversion table
| Miles per gallon (UK) (mpg (UK)) | Miles per gallon (US) (mpg (US)) |
|---|---|
| 1 | 0.832674 |
| 2 | 1.665348 |
| 3 | 2.498023 |
| 5 | 4.163371 |
| 10 | 8.326742 |
| 20 | 16.653484 |
| 50 | 41.633709 |
| 100 | 83.267418 |
| 500 | 416.337092 |
| 1,000 | 832.674185 |
The formula
To convert MPG (UK) to MPG (US), multiply the imperial figure by 0.8326742:
MPG (US) = MPG (UK) × 0.8326742
A worked example
Say a car is rated at 40 MPG (UK) and you want the US number:
40 × 0.8326742 = 33.31 MPG (US)
So 40 MPG (UK) is about 33.31 MPG (US) — the same car, a smaller number.
Why it's an approximation
The two figures use different gallons. The imperial (UK) gallon is about 20% larger than the US gallon, so a UK MPG figure is about 20% higher than the US MPG for the very same car. When you go from UK to US, you're dividing the same distance by a smaller gallon, so the miles-per-gallon number gets smaller. The factor 0.8326742 captures that gap, but it's a rounded value — the underlying gallon ratio doesn't come out clean — so treat the result as approximate.
When you'll use it
Comparing a UK car listing or brochure against US fuel-economy numbers, reading an imported car's imperial rating in US terms, or making sense of a review that quotes MPG in the UK sense.
Frequently asked questions
Why is the US MPG lower than the UK MPG for the same car?
Because the imperial (UK) gallon is about 20% larger than the US gallon. A UK gallon holds more fuel, so a car goes further on 'one gallon' in the UK sense — which makes the UK MPG figure about 20% higher than the US MPG for the exact same car. Going UK to US, the number gets smaller.
How many MPG (US) is 40 MPG (UK)?
About 33.31 MPG (US). Multiply 40 by 0.8326742 to get 33.31 — noticeably lower, because the US gallon is the smaller one.
Is the MPG (UK) to MPG (US) conversion exact?
No. The factor 0.8326742 is rounded, because the UK and US gallons don't divide into a clean ratio. For everyday comparisons it's close enough, but it stays an approximation.