What it does
Enter how far you are going, how much fuel your vehicle uses and what fuel costs, and the page tells you the fuel for the trip and the money it will cost. It understands the four ways the world measures fuel economy and both gallons, so you can use the figures exactly as they appear on your dashboard, in your manual or at the pump. It works for a car, a motorbike or a truck.
A second box converts between the four economy units, handy when comparing a UK car with a US one. If the trip shares the cost, the percentage calculator helps with rounding up a fair extra for the driver, and the budget planner with the month’s travel.
How to use it
- Type the distance and choose km or miles.
- Type the fuel economy and pick its unit.
- Type the fuel price and say whether it is per litre, per US gallon or per UK gallon.
- Tick round trip to double the distance, and enter how many people share the cost.
What the units mean
- L/100 km: litres used per 100 km. Lower is better.
- km/L: kilometres per litre. Higher is better.
- mpg (US) and mpg (UK): miles per gallon. A UK gallon is bigger, so the same car shows a bigger UK number.
Worked example
A 100 km trip in a car that uses 8 L/100 km needs 8 litres. At 1.50 a litre the fuel costs 12.00. As a round trip it is 24.00, or 12.00 each for two people. In the converter, 8 L/100 km is 29.4 mpg (US), 35.3 mpg (UK) or 12.5 km/L.
FAQs
Why does my mpg look different from my friend’s? US and UK gallons are different sizes. Check which one the figure uses.
How accurate is it? It is an estimate. Speed, load, hills, weather and traffic all change real fuel use, so add a little margin.
Does it include tolls or wear? No, only fuel.
Where the numbers come from
- Conversions: 1 mile = 1.609344 km, 1 US gallon = 3.785411784 L, 1 UK (imperial) gallon = 4.54609 L (international standard definitions).
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-10.