Conversion formulas
L/100 km = 235.215 ÷ US mpg
L/100 km = 282.481 ÷ UK mpg
km/L = 100 ÷ (L/100 km)
UK mpg = US mpg × 1.20095
A US gallon is 3.785 liters while an imperial (UK) gallon is 4.546 liters, which is why the same car shows a higher mpg figure in the UK.
Why mpg and L/100 km work in opposite directions
Miles per gallon measures distance per fuel – higher is better. Liters per 100 km measures fuel per distance – lower is better. Because the relationship is inverse, improving from 10 to 20 mpg saves far more fuel than improving from 40 to 50 mpg.
Quick reference table
| US mpg | L/100 km | UK mpg | km/L |
|---|---|---|---|
| 15 | 15.7 | 18.0 | 6.4 |
| 20 | 11.8 | 24.0 | 8.5 |
| 25 | 9.4 | 30.0 | 10.6 |
| 30 | 7.8 | 36.0 | 12.8 |
| 35 | 6.7 | 42.0 | 14.9 |
| 40 | 5.9 | 48.0 | 17.0 |
| 50 | 4.7 | 60.0 | 21.3 |
Every value from 10 to 60 mpg
Frequently asked questions
How do I convert mpg to L/100 km?
Divide 235.215 by the US mpg figure. For example, 30 mpg = 235.215 ÷ 30 = 7.84 L/100 km.
Why is UK mpg higher than US mpg?
The imperial gallon is about 20% larger than the US gallon, so a car travels further on one UK gallon.
What is good fuel economy?
For a gasoline car, more than 35 US mpg (under 6.7 L/100 km) is very good. Hybrids often exceed 50 mpg.
Which countries use L/100 km?
Canada, most of Europe, Australia and many other countries use liters per 100 km. The US and the UK use mpg, with different gallons.
Last updated November 10, 2026