UK MPG
Miles travelled per imperial gallon. Higher is better. One imperial gallon is 4.54609 litres.
UK MPG, US MPG and L/100km explained
Fuel economy numbers can look similar while using different gallons or the opposite direction of measurement. This page puts the three common formats on the same footing.
Reviewed 6 September 2026UK units unless statedCalculations and assumptions shown
Three measures, two different ideas
US MPG
Miles travelled per US gallon. Higher is better, but the US gallon is smaller, so the numeric MPG is lower for the same fuel consumption.
L/100km
Litres used to travel 100 km. Lower is better, so the direction is reversed compared with MPG.
Useful formulas
L/100km = 282.481 ÷ UK MPG
UK MPG = 282.481 ÷ L/100km
US MPG ≈ UK MPG × 0.832674
UK fuel-economy reference table
The last two columns also show what 100 miles costs at 145p/litre, making the efficiency difference easier to visualise.
| UK MPG | L/100km | Litres / 100 miles | Cost / 100 miles at 145p/L |
|---|---|---|---|
| 25 | 11.3 | 18.2 L | £26.37 |
| 30 | 9.4 | 15.2 L | £21.97 |
| 35 | 8.1 | 13.0 L | £18.83 |
| 40 | 7.1 | 11.4 L | £16.48 |
| 45 | 6.3 | 10.1 L | £14.65 |
| 50 | 5.6 | 9.1 L | £13.18 |
| 55 | 5.1 | 8.3 L | £11.99 |
| 60 | 4.7 | 7.6 L | £10.99 |
| 70 | 4.0 | 6.5 L | £9.42 |
Example: why 50 MPG can mean different things
50 UK MPG is about 5.65 L/100km. The same consumption is about 41.6 US MPG. A US website quoting “50 MPG” therefore describes better fuel economy than a UK website quoting 50 imperial MPG.
When comparing vehicles or forum posts, identify the gallon before comparing the number. The country of the source is often a clue, but the unit label is better evidence.
Why L/100km can make fuel savings easier to see
MPG is a reciprocal measure, so a 10 MPG improvement does not represent a fixed fuel saving. Moving from 20 to 30 MPG saves much more fuel than moving from 50 to 60 MPG over the same distance. L/100km expresses consumption directly, which makes absolute fuel differences easier to compare.