Fuel economy is published in two opposite ways. The United States and the United Kingdom quote distance per fuel (miles per gallon, with two different gallons), while Canada, Europe, Australia and most of the world quote fuel per distance (liters per 100 kilometers). This converter handles all of them, plus kilometers per liter, miles per liter and the gallons-per-100-miles figure printed on current US window stickers.
How to use the fuel economy converter
- Enter the fuel economy figure you have.
- Choose its unit in From, such as miles per gallon (US) or liters per 100 kilometers.
- Choose the unit you want in To. The result appears instantly, with the same figure in every unit in the table below.
- Check the extra rows: gallons per 100 miles, the fuel needed for 10,000 miles or kilometers, and the carbon dioxide released per mile if the fuel is gasoline.
Why the conversion is a division
Miles per gallon and liters per 100 km are reciprocals, so you cannot convert them with a single multiplier the way you convert inches to centimeters. The two constants come straight from exact unit definitions (1 mile = 1.609344 km, 1 US gallon = 3.785411784 L, 1 imperial gallon = 4.54609 L):
Internally the calculator turns every figure into kilometers per liter first, then into the unit you asked for, so any pair of units works.
Worked example
A US sedan is rated at 30 mpg combined.
L/100 km: 235.215 ÷ 30 = 7.84 L/100 km.
UK mpg: 30 × 1.20095 = 36.03 mpg (UK) — the same car, a bigger gallon.
Fuel for 10,000 miles: 10,000 ÷ 30 = 333.3 US gallons, or about 1,262 liters.
CO₂: the EPA estimates 8,887 grams of CO₂ per gallon of gasoline burned, so 8,887 ÷ 30 ≈ 296 g per mile.
Going the other way, a European hatchback listed at 6.5 L/100 km works out to 235.215 ÷ 6.5 = 36.19 US mpg.
Common values
| US mpg | L/100 km | km/L | UK mpg |
|---|---|---|---|
| 15 | 15.68 | 6.38 | 18.0 |
| 20 | 11.76 | 8.50 | 24.0 |
| 25 | 9.41 | 10.63 | 30.0 |
| 30 | 7.84 | 12.75 | 36.0 |
| 40 | 5.88 | 17.01 | 48.0 |
| 50 | 4.70 | 21.26 | 60.0 |
The mpg illusion
Because mpg is a reciprocal, equal mpg gains are not equal fuel savings. Over 10,000 miles a 10 mpg truck burns 1,000 gallons and a 20 mpg truck burns 500, a saving of 500 gallons. Upgrading a 30 mpg car to 60 mpg saves only 333 − 167 = 167 gallons. If you are choosing between replacing a thirsty vehicle and a fairly efficient one, the thirsty one usually saves more fuel. That is why the US EPA label also shows gallons per 100 miles, and why this converter lists it on every result.
Things to watch
- Check which gallon a source uses. British magazines and UK government figures use imperial gallons; US sources and window stickers use US gallons.
- Electric vehicles are rated in miles per gallon equivalent (MPGe), based on 33.7 kWh per gallon of gasoline, or in kWh per 100 miles. Those are energy figures, not fuel volumes, and are not converted here.
- Ratings are averages. Highway driving, cold weather, roof racks and tire pressure all move real-world economy away from the label.
To turn an mpg figure into a trip cost, use the gas mileage calculator. For plain volume or distance conversions, see gallons to liters and miles to kilometers.
Frequently asked questions
How do I convert mpg to L/100 km?
Divide 235.215 by the US mpg figure. 30 mpg is 235.215 ÷ 30 = 7.84 L/100 km. For UK (imperial) mpg, divide 282.481 by the mpg figure instead.
Why is the US mpg different from the UK mpg?
The UK imperial gallon is 4.54609 liters, about 20% larger than the 3.785411784-liter US gallon. A car that goes 30 miles on a US gallon goes about 36 miles on an imperial gallon, so UK mpg figures always look higher.
Is a lower L/100 km number better?
Yes. L/100 km measures fuel used per distance, so smaller is more efficient. Miles per gallon and km/L measure distance per fuel, where bigger is better.
What is the 'mpg illusion'?
Fuel saved does not grow in step with mpg. Going from 10 to 20 mpg saves 500 gallons over 10,000 miles, while going from 30 to 60 mpg saves only about 167 gallons. Fuel-per-distance figures such as gallons per 100 miles show the real savings directly.