Calculators & everyday math
US MPG vs. UK Imperial MPG: Why the Numbers Differ
A car that gets 30 miles per gallon in the US gets about 36 miles per gallon in the UK — without driving any differently. The miles are the same; the gallons are not. This guide explains the two gallons, how to convert between the MPG figures, and how to tell which one a number uses.
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Two different gallons
The US gallon is defined as 231 cubic inches, exactly 3.785411784 liters — a size inherited from the old English wine gallon. The UK imperial gallon was set in 1824 as the volume of 10 pounds of water and is now exactly 4.54609 liters. The imperial gallon is about 20% larger, so a car covers about 20% more miles on it.
The conversion factors
Both MPG figures measure distance per fuel, so converting between them is a plain multiplication.
- 1 MPG (US) = 1.200949926 MPG (Imperial/UK)
- 1 MPG (Imperial/UK) = 0.8326741846 MPG (US)
US MPG to imperial MPG
| MPG (US) | MPG (Imperial/UK) |
|---|---|
| 20 | 24.01899851 |
| 25 | 30.02374814 |
| 30 | 36.02849777 |
| 40 | 48.03799702 |
| 50 | 60.04749628 |
Imperial MPG to US MPG
| MPG (Imperial/UK) | MPG (US) |
|---|---|
| 40 | 33.30696739 |
| 50 | 41.63370923 |
| 60 | 49.96045108 |
How to tell which MPG you have
- US window stickers, US reviews, and US government ratings use US gallons.
- UK brochures, UK reviews, and UK government figures use imperial gallons.
- Older Canadian figures may be in imperial MPG; current Canadian ratings lead with L/100 km.
- When a source doesn’t say, check its country — or compare in L/100 km, which has only one version.
US vs. UK MPG FAQ
- Why is UK MPG higher than US MPG for the same car?
- The imperial gallon is about 20% larger than the US gallon, so more miles fit in each one.
- How do I convert UK MPG to US MPG?
- Multiply by 0.8326741846. For example, 50 UK MPG is about 41.63 US MPG.
- How do I convert US MPG to UK MPG?
- Multiply by 1.200949926. For example, 30 US MPG is about 36.03 UK MPG.
- Are UK and US miles the same?
- Yes. Both use the international mile of exactly 1.609344 km; only the gallon differs.
- Why do European cars sometimes seem more economical in UK reviews?
- Partly the larger gallon, and partly different official test cycles. Converting the unit fixes the first difference, not the second.
Related guides
- MPG vs. L/100 kmHow miles per gallon and liters per 100 km measure fuel economy in opposite ways, the reciprocal formula, and conversion tables both ways.
- Why Lower L/100 km Is BetterFuel per distance versus distance per fuel, the MPG illusion, and why liters per 100 km makes fuel savings easier to compare.
Open the tool
Jump into Fuel Economy Converter when you are ready to process your files.
