American cars quote miles per gallon, British ones miles per imperial gallon, much of Europe litres per 100 kilometres, and others kilometres per litre. Worse, three of those go up as efficiency improves and one goes down. This converter lines all four up, so you can compare an imported car's figures without guessing.
How to use it
- Enter the fuel economy figure you have.
- Choose the unit it's in.
- Choose the unit you want to see.
- Read the result and the others.
When it helps
- Comparing a US car's mpg with a European car's L/100 km.
- Checking fuel-cost estimates across markets.
- Understanding an imported vehicle's specification sheet.
- Comparing figures from different sources.
Good to know
- Higher mpg and km/L mean better economy, but a lower L/100 km number is the better one.
- US mpg looks lower than UK mpg for the same car because the US gallon is smaller.
- As a quick estimate, 235.2 divided by the US mpg figure gives L/100 km: 30 mpg is about 7.8.
How the conversion works
The tool converts through kilometres per litre. A US mile per gallon is 0.4251 km/L, and an imperial mile per gallon is 0.3540 km/L. Litres per 100 kilometres is the inverse: 100 divided by the km/L figure. That inverse relationship is why the numbers move in opposite directions.
Because of that, you can't convert by a constant factor between L/100 km and mpg. Instead, you divide a constant by the number, which is the 235.2 shortcut for US mpg.
Worked example: comparing two cars
Car A is rated 35 mpg (US) and car B 7.5 L/100 km. Convert A to L/100 km and you get 6.7. So car A uses less fuel, 6.7 litres for every 100 kilometres against 7.5. Over 15,000 km a year, the difference is 120 litres.
Multiply by the price of fuel to put a money figure on it. At 1.60 per litre, that's 192 a year, which is useful to know when choosing between two similar vehicles.
Why L/100 km is more useful
Fuel used per distance is easier to reason about than distance per fuel. Improving from 10 to 20 mpg saves far more fuel than improving from 30 to 40, even though both are a ten-point gain. In L/100 km the effect is clear: 23.5 down to 11.8 saves almost 12 litres per 100 km, while 7.8 down to 5.9 saves only about 2.
That's why many countries and regulators use consumption in litres per 100 kilometres, and why mpg figures can mislead if you're comparing efficient cars.
Real-world factors
Official figures come from laboratory tests that usually flatter reality. Driving style, tyre pressure, load, air conditioning and short trips all raise consumption, sometimes by 20 percent or more. Treat the rated figure as a comparison tool rather than a promise.
Electric vehicles use kilowatt-hours per 100 km or miles per kWh. A rough rule is that 1 US gallon of petrol holds about 33.7 kWh of energy, which is the basis for the miles per gallon equivalent you see on electric car labels.
Questions
Why do UK and US mpg figures differ?
The imperial gallon is about 20 percent larger than the US one.
What if I enter zero?
A zero figure has no meaningful L/100 km equivalent, so you get a dash instead.