Fuel Economy Converter
mpg (US and UK), L/100km and km/L, including the inverse maths that trips people up
mpg (US and UK), L/100km and km/L, including the inverse maths that trips people up. No data leaves your browser – every conversion happens locally.
Distance per fuel versus fuel per distance
MPG and km/L tell you how far you go on a unit of fuel, so higher is better. L/100km tells you how much fuel a set distance takes, so lower is better. Because they're inverses, the converter divides rather than multiplies: L/100km = 235.21 ÷ mpg (US).
Gallons differ too. A UK gallon is 4.546 L and a US gallon 3.785 L, so the same car is rated at about 20% more mpg in the UK. 40 mpg (US) is 48 mpg (UK).
Official figures (ARAI in India, EPA in the US, WLTP in Europe) are lab results, and real-world economy is usually 10–25% worse. Electric and CNG vehicles use different units (kWh/100 km, km/kg) and aren't covered.
Fuel economy conversions
| 30 mpg (US) | 7.84 L/100km |
| 40 mpg (US) | 5.88 L/100km |
| 6 L/100km | 39.2 mpg (US) |
| 8 L/100km | 29.4 mpg (US) |
| 10 L/100km | 23.5 mpg (US) |
Good to know
Higher is better for mpg, lower is better for L/100km
With MPG (miles per gallon), more miles per gallon means more efficient. With L/100km, fewer liters per 100 km = more efficient. They're inverses of each other, which is why comparing them is confusing.
US mpg vs UK mpg
A US gallon is 3.785 liters. A UK gallon is 4.546 liters. A car rated at 40 mpg (US) is 48 mpg (UK). Always check which gallon a fuel economy figure uses.
Worked examples
An Indian hatchback
A claimed 18 km/L is 5.56 L/100km or 42.3 mpg (US). Expect closer to 14–15 km/L in city traffic.
A US pickup
25 mpg (US) is 9.41 L/100km. That's a useful number if you're comparing it to a European brochure.
UK versus US reviews
A car tested at 48 mpg in a British review and 40 mpg in an American one is the same car. Only the gallon changed.
L/100km, mpg and km/L side by side
This is the table for comparing brochures and reviews from different countries. Each row starts from litres per 100 km, then works out US mpg (235.21 ÷ L/100km), UK mpg and km/L (100 ÷ L/100km).
| L/100km | mpg (US) | mpg (UK) | km/L |
|---|---|---|---|
| 4 | 58.8 | 70.6 | 25.0 |
| 5 | 47.0 | 56.5 | 20.0 |
| 6 | 39.2 | 47.1 | 16.7 |
| 7 | 33.6 | 40.4 | 14.3 |
| 8 | 29.4 | 35.3 | 12.5 |
| 9 | 26.1 | 31.4 | 11.1 |
| 10 | 23.5 | 28.2 | 10.0 |
| 12 | 19.6 | 23.5 | 8.3 |
| 15 | 15.7 | 18.8 | 6.7 |
Averaging mpg gives the wrong answer
Say you drive 100 miles at 20 mpg and another 100 at 40 mpg. The average looks like 30 mpg, but it isn't. The first leg burns 5 gallons and the second 2.5, so 200 miles takes 7.5 gallons, which is 26.7 mpg. Averaging mpg figures always overstates economy when the distances are equal.
L/100km doesn't have this problem, since it measures fuel per distance and averages correctly over equal distances. It's one reason fuel-per-distance units make it easier to see what an upgrade really saves: going from 15 to 10 L/100km saves more fuel than going from 6 to 4.