UK MPG to US MPG Converter
Convert imperial miles per gallon to US miles per gallon — the same car reads about 20% lower in the US. Results update as you type; exact factors shown.
One miles per imperial gallon is 0.8327 miles per US gallon — see the exact factor, not a rounded rule of thumb.
How the uk mpg to us mpg converter works
Fuel economy is an inverse quantity: lower L/100 km is better, higher mpg is better. mpg (US) = 235.215 / (L/100 km) because a US gallon is 3.785 L and a mile 1.609 km; mpg (UK) = 282.481 / (L/100 km) with the 4.546 L imperial gallon. UK mpg figures are therefore always 20% higher than US mpg for the same car.
The UK is metric for most trade and science but keeps miles, pints, stone and mpg (with the imperial gallon) in daily life.
Common fuel economy conversions
| From | To | Units |
|---|---|---|
| 20 mpg (UK) | 16.6535 mpg (US) | miles per imperial gallon to miles per US gallon |
| 25 mpg (UK) | 20.8169 mpg (US) | miles per imperial gallon to miles per US gallon |
| 30 mpg (UK) | 24.9802 mpg (US) | miles per imperial gallon to miles per US gallon |
| 35 mpg (UK) | 29.1436 mpg (US) | miles per imperial gallon to miles per US gallon |
| 40 mpg (UK) | 33.307 mpg (US) | miles per imperial gallon to miles per US gallon |
| 45 mpg (UK) | 37.4703 mpg (US) | miles per imperial gallon to miles per US gallon |
| 50 mpg (UK) | 41.6337 mpg (US) | miles per imperial gallon to miles per US gallon |
| 55 mpg (UK) | 45.7971 mpg (US) | miles per imperial gallon to miles per US gallon |
| 60 mpg (UK) | 49.9605 mpg (US) | miles per imperial gallon to miles per US gallon |
| 70 mpg (UK) | 58.2872 mpg (US) | miles per imperial gallon to miles per US gallon |
| 80 mpg (UK) | 66.6139 mpg (US) | miles per imperial gallon to miles per US gallon |
| 100 mpg (UK) | 83.2674 mpg (US) | miles per imperial gallon to miles per US gallon |
Units in this converter and their exact factors
| Unit | Symbol | To L/100 km |
|---|---|---|
| litres per 100 km | L/100 km | x |
| kilometres per litre | km/L | 100÷x |
| miles per imperial gallon | mpg (UK) | 282.480936÷x |
| miles per US gallon | mpg (US) | 235.214583÷x |
FAQFrequently asked questions about fuel economy conversion
Why do UK mpg figures look better?
Because an imperial gallon is 4.546 L against the US 3.785 L — 20% more fuel per gallon, so 20% more miles.
What is 50 UK mpg in US mpg?
41.6 US mpg.
Which gallon is bigger?
The imperial, by about 20%.
Does this affect fuel prices too?
Yes — a price per imperial gallon is not comparable to a price per US gallon either.
What is 40 UK mpg in L/100km?
7.06 L/100km.
Where these figures come from
- BIPM — The International System of Units (SI Brochure, 9th edition) — definitions of the base and derived units.
- NIST Special Publication 811 — Guide for the Use of the International System of Units — the exact conversion factors used here.
- National Physical Laboratory (NPL) — United Kingdom's national measurement authority.
Last checked: September 2026. Conversion factors are fixed by definition and do not change with tax years or regulations.