MPG to L/100 km: How to Compare Fuel Economy Across Countries
Fuel economy is reported in miles per gallon (mpg) in the US and UK, and in liters per 100 kilometers (L/100 km) in most of Europe, Canada and Australia. The two measures run in opposite directions: a higher mpg is better, while a lower L/100 km is better. They also use different gallons in the US and UK, which makes comparing cars across countries confusing.
The formulas
Because mpg is distance per volume and L/100 km is volume per distance, the conversion is a reciprocal, not a simple multiplication:
- US mpg to L/100 km: divide 235.215 by the mpg figure.
- UK (imperial) mpg to L/100 km: divide 282.481 by the mpg figure.
- L/100 km to US mpg: divide 235.215 by the L/100 km figure.
For example, 30 US mpg is 235.215 ÷ 30 = 7.84 L/100 km. And 7 L/100 km is 235.215 ÷ 7 = 33.6 US mpg.
Quick chart
| L/100 km | US mpg | UK mpg |
|---|---|---|
| 4 | 58.8 | 70.6 |
| 5 | 47.0 | 56.5 |
| 6 | 39.2 | 47.1 |
| 7 | 33.6 | 40.4 |
| 8 | 29.4 | 35.3 |
| 10 | 23.5 | 28.2 |
| 12 | 19.6 | 23.5 |
| 15 | 15.7 | 18.8 |
The US vs UK gallon trap
A UK (imperial) gallon is 4.546 liters, while a US gallon is 3.785 liters, about 20 percent smaller. So a car that gets 40 mpg in a UK test gets only about 33 mpg in US terms, though it burns exactly the same fuel. When you read mpg figures, check which gallon the source uses. You can compare the volumes with our liters to gallons converter.
Why L/100 km is more useful
L/100 km measures fuel used per distance, so it adds up in a straight line. Replacing a car that does 10 L/100 km with one that does 8 saves 2 liters every 100 km. Mpg works the other way around: going from 15 to 20 mpg saves more fuel than going from 40 to 50 mpg, which surprises many people. This is called the “mpg illusion”.
Estimating running costs
Multiply the L/100 km figure by the price per liter to get the cost of 100 km. At 7 L/100 km and a price of 1.80 per liter, 100 km costs 12.60. In the US, divide the price per gallon by the mpg to get cost per mile.