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 US uses customary units (US gallon, short ton, °F) in daily life; NIST SP 811 gives the exact SI factors.
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 |
|---|---|---|
| liters per 100 km | L/100 km | x |
| kilometers per liter | 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 Institute of Standards and Technology (NIST) — United States's national measurement authority.
Last checked: September 2026. Conversion factors are fixed by definition and do not change with tax years or regulations.