How to use the fuel economy converter
- Choose the unit of the figure you have: US MPG, UK MPG, litres per 100 km or kilometres per litre.
- Type the number, for example 30 or 7.5.
- Read every other unit at once. The top line shows the most useful conversion for your starting unit.
- Use Copy result to paste the conversions into a note or a message.
The conversion formulas
L/100 km = 282.481 ÷ UK MPG
km/L = 100 ÷ L/100 km
UK MPG = US MPG × 1.20095
US gallons per 100 miles = 100 ÷ US MPG
The constants come from exact definitions: a US gallon is 3.785411784 litres, a UK gallon is 4.54609 litres and a mile is 1.609344 km. Note that MPG and km/L measure distance per fuel (higher is better), while L/100 km and gallons per 100 miles measure fuel per distance (lower is better), so the scales run in opposite directions.
Worked example
A car rated at 30 miles per US gallon:
- Litres per 100 km: 235.215 ÷ 30 = 7.84 L/100 km.
- UK MPG: 282.481 ÷ 7.84 = 36.03 UK MPG, about 20% higher because the UK gallon is larger.
- Kilometres per litre: 100 ÷ 7.84 = 12.75 km/L.
- US gallons per 100 miles: 100 ÷ 30 = 3.33 gal.
Tips for comparing cars
- Compare fuel per distance. Improving from 10 to 20 MPG saves far more fuel than going from 30 to 40 MPG. Gallons per 100 miles or L/100 km show that difference honestly.
- Compare like with like. US EPA ratings, the European and UK WLTP figures and older NEDC figures come from different test cycles, so the same car can show different numbers.
- Watch the gallon. Car reviews from the UK and the US both say “MPG” but mean different gallons; convert before comparing.
- Use your own data. Fill-up records over a few tanks give the most realistic figure for your driving.
- MPGe is different. US labels for electric cars show MPGe, which counts 33.7 kWh of electricity as one gallon of gasoline. It compares energy use, not running cost, so use the EV charging calculator for money.
US, UK and Canada differences
The United States uses miles per US gallon, and its window stickers also show gallons per 100 miles. The UK sells fuel in litres but advertises economy in miles per imperial gallon, using WLTP test results. Canada’s official fuel consumption ratings are published in L/100 km, often with an MPG figure alongside, because many Canadians are used to both.
Metric units and other countries
Most of Europe, Australia and many other countries use L/100 km. Kilometres per litre is common in Pakistan, India, Japan, Indonesia and parts of Latin America. Whatever your country, the conversions here are exact, so the same car gives consistent figures in every unit. If you are importing a car or reading a foreign review, convert its figure first, then compare it with cars sold locally.