Fuel Economy Converter
Convert fuel economy between miles per gallon, liters per 100 km, and km per liter.
How to use the fuel economy converter
Enter a number, pick the unit you have, and choose the unit you want. The result updates as you type, and the swap button flips the two units to read it the other way.
Mind the gallon. A US gallon is smaller than a UK gallon, so 30 mpg in the US is not 30 mpg in Britain. This tool keeps the two separate so the numbers stay honest.
Common fuel economy conversions
| 30 mpg (US) | 7.84 L/100km |
| 40 mpg (US) | 5.88 L/100km |
| 50 mpg (US) | 4.70 L/100km |
| 5 L/100km | 47.0 mpg (US) |
| 8 L/100km | 29.4 mpg (US) |
| 15 km/L | 6.67 L/100km |
Why mpg and L/100km move in opposite directions
Miles per gallon counts distance per unit of fuel, so a higher number means a thriftier car. Liters per 100 km counts fuel per fixed distance, so there a lower number is better.
Because one measures distance over fuel and the other fuel over distance, they are inverses. You cannot convert with a single multiplier, which is why this tool divides through a shared figure rather than scaling by a constant.
Frequently asked questions
- How do I convert mpg to L/100km?
- Divide 235.21 by the US mpg figure. So 30 mpg (US) is about 7.84 L/100km. The relationship is a division because the two units are inverses.
- Why are US and UK mpg different?
- The gallon differs. A US gallon is 3.785 liters, while a UK gallon is 4.546 liters. The same car shows a higher mpg in the UK simply because the gallon is bigger.
- Is a lower L/100km better?
- Yes. Liters per 100 km measures fuel used over a set distance, so less fuel means a lower number and a more efficient car. With mpg it is the reverse.
- What is km/L?
- Kilometers per liter is the metric version of mpg, common in parts of Asia. Like mpg, a higher number is better. It converts to L/100km by dividing 100 by the figure.