MPG to L/100km Converter
Convert MPG to L/100 km (both US and UK gallon variants) for comparing US car reviews against European spec sheets and translating fuel efficiency data.
Last updated: May 2026
Enter a value to see the conversion instantly.
Quick reference
| US MPG | L/100km |
|---|---|
| 20 | 11.76 |
| 30 | 7.84 |
| 40 | 5.88 |
| 50 | 4.70 |
Why the two scales move in opposite directions
Miles per gallon measures distance per fixed amount of fuel, so a bigger number is better. Litres per 100 km measures fuel for a fixed distance, so a smaller number is better. That is why they are not a straight ratio and why converting by eye is unreliable.
The exact relationship for US gallons is L/100km = 235.215 divided by MPG. A car rated at 30 US MPG works out to 235.215 / 30, which is about 7.84 L/100km. Double the efficiency to 60 MPG and the figure roughly halves to about 3.92 L/100km, which shows how the scale compresses at the efficient end.
Watch the gallon definition. A US gallon is smaller than a UK imperial gallon, so the same car shows a higher MPG number in UK figures. This page uses the US gallon, so compare like with like before trusting a result.
Frequently asked questions
Does this page use US or UK MPG?
This version uses US MPG. UK MPG is different and always gives a larger number for the same car. Mixing them up gives bad comparisons.
Why is this better than rounding roughly in my head?
Because fuel economy comparisons are easy to misread. One exact conversion prevents bad assumptions when you are comparing test results, ads or travel budgets.
What is a decent modern petrol number?
For many regular petrol cars, something around 5 to 7.5 L/100km is generally respectable. Heavier SUVs and performance cars will usually sit higher.