Fuel Economy Converter
Enter a fuel economy figure and choose its unit. We convert it to the other three.
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The formula
L/100 km = 235.215 / mpg (US). mpg (US) = 235.215 / (L/100 km). mpg (UK) = 282.481 / (L/100 km).
Why the units differ
The US measures how far you go on a fixed amount of fuel (miles per gallon), so a bigger number is better. Most of Europe and Asia measure how much fuel you use over a fixed distance (litres per 100 km), so a smaller number is better. And the UK gallon is bigger than the US one, so 40 mpg in the UK is about 33 mpg in the US.
A table to remember
| mpg (US) | L/100 km |
|---|---|
| 15 | 15.7 |
| 20 | 11.8 |
| 25 | 9.4 |
| 30 | 7.8 |
| 40 | 5.9 |
| 50 | 4.7 |
Not a straight line
Because one is the inverse of the other, small gains matter more at the low end. Going from 15 to 20 mpg saves far more fuel over 10,000 miles than going from 40 to 45.
Examples to check
Type these into the calculator above to see how it behaves. Every result below was produced by the same calculator code that runs on this page.
| What you enter | What you get |
|---|---|
| Value: 30; Miles per US gallon (mpg) | Litres per 100 km: 7.84; Miles per US gallon: 30 |
| Value: 8; Litres per 100 km | Litres per 100 km: 8; Miles per US gallon: 29.402 |
| Value: 45; Miles per UK gallon | Litres per 100 km: 6.277; Miles per US gallon: 37.47 |
Fuel Economy Converter: frequently asked questions
What is a good fuel economy?
Around 30 mpg (US), or about 8 L/100 km, is typical for a petrol car. Hybrids reach 50 mpg (4.7 L/100 km) or better.
Why is UK mpg higher than US mpg?
The imperial gallon is about 20 percent bigger, so the same car gets a higher mpg figure in the UK.
How exact is the conversion?
It uses the internationally agreed definitions, and rounds only the number you see.
Is what I enter in this converter saved or sent anywhere?
No. The calculation runs in your browser, so what you enter is not sent to our servers. We only count, anonymously, whether a tool ran successfully.
Is this converter free to use?
Yes. It is free, needs no sign-up and has no usage limit.
Last reviewed: October 3, 2026