Car fuel economy is quoted as miles per gallon (mpg) in the US and UK, liters per 100 km in Europe and Australia, and kilometers per liter in much of Asia. Comparing them is confusing — this guide makes it simple.
In this guide
- Why the units work differently
- The formulas
- Fuel economy chart
- US mpg vs UK mpg
- Convert instantly
Why the units work differently
mpg and km/L measure distance per fuel (higher is better). L/100km measures fuel per distance (lower is better). Because one is the inverse of the other, the conversion is a division, not a simple multiplication.
The formulas
- L/100km = 235.215 ÷ US mpg
- L/100km = 282.481 ÷ UK mpg
- L/100km = 100 ÷ km/L
Fuel economy chart
| US mpg | UK mpg | L/100km | km/L |
|---|---|---|---|
| 15 | 18 | 15.7 | 6.4 |
| 20 | 24 | 11.8 | 8.5 |
| 25 | 30 | 9.4 | 10.6 |
| 30 | 36 | 7.8 | 12.8 |
| 40 | 48 | 5.9 | 17 |
| 50 | 60 | 4.7 | 21.3 |
US mpg vs UK mpg
A UK (imperial) gallon is 4.546 liters, while a US gallon is 3.785 liters. So the same car shows about 20% higher mpg in the UK. Always check which gallon a figure uses.
Convert instantly
Use our US mpg to L/100km, UK mpg to L/100km and km/L to mpg converters.
Frequently asked questions
Is 30 mpg good?
For a petrol car, 30 US mpg (7.8 L/100km) is reasonable; hybrids often exceed 45 mpg.
What is 6 L/100km in mpg?
About 39 US mpg or 47 UK mpg.
Why do official figures differ from real life?
Lab test cycles rarely match real driving, traffic, speed and air-conditioning use.
