Fuel Cost Calculator
Work out how much fuel a trip will use and what it will cost - in US mpg, UK mpg or L/100 km - and split it between passengers.
Distance ÷ fuel economy × price · By Stuart Mathieson · Updated October 2026
One way
Results
Fuel Cost
Cost per Person
Fuel Used
Cost per Distance
Trip:
Fuel economy:
Real fuel use depends on speed, traffic, load, weather and the vehicle's condition, so treat the result as an estimate.
How the fuel cost calculator works
The calculator works out how much fuel the trip needs from the distance and your vehicle's fuel economy, then multiplies by the fuel price. It handles the three common ways of measuring fuel economy:
A US gallon is exactly 3.785411784 liters, and a UK (imperial) gallon 4.54609 liters - about 20% bigger. That's why the same car shows a higher mpg figure in the UK than in the US. UK fuel is sold by the litre, but fuel economy is still quoted in miles per gallon, so the calculator converts between the two for you.
Worked examples
- US: a 300-mile trip in a car that does 28 mpg uses 10.71 gallons. At $3.50 a gallon, that's $37.50.
- UK: 300 miles at 45 mpg uses 30.31 litres. At £1.40 a litre, that's £42.43.
- Metric: 500 km at 6.5 L/100 km uses 32.5 litres. At €1.75 a litre, that's €56.88.
Tick Round trip to double the distance, and enter the number of people to see each person's share.
Converting fuel economy
mpg measures how far you go on a gallon - higher is better. L/100 km measures how much fuel you use to go 100 km - lower is better. To convert:
| L/100 km | US mpg | UK mpg |
|---|---|---|
| 4 | 58.8 | 70.6 |
| 5 | 47.0 | 56.5 |
| 6 | 39.2 | 47.1 |
| 8 | 29.4 | 35.3 |
| 10 | 23.5 | 28.2 |
| 12 | 19.6 | 23.5 |
Getting a realistic fuel economy figure
- In the US, fueleconomy.gov lists official EPA ratings for most cars sold since 1984. Use the highway figure for long road trips and the city or combined figure for town driving.
- Official figures are measured in standard lab tests, and many drivers get a little less on the road. Your own figure - from your trip computer, or from distance driven between fill-ups - is usually the best guide.
- High speeds, roof boxes, heavy loads, cold weather and air conditioning all increase fuel use.
Frequently asked questions
How do I calculate the fuel cost of a trip?
Divide the distance by your car's fuel economy to get the fuel used, then multiply by the price. A 300-mile trip at 28 mpg uses 10.71 gallons, which costs $37.50 at $3.50 a gallon.
Why is UK mpg higher than US mpg for the same car?
A UK (imperial) gallon is 4.54609 liters, about 20% more than a US gallon of 3.785411784 liters, so a car goes further on a UK gallon. 30 US mpg is about 36 UK mpg.
How do I convert mpg to L/100 km?
Divide 235.215 by US mpg, or 282.481 by UK mpg. 30 US mpg is 7.84 L/100 km.
Does it work for electric cars?
Not directly - this calculator uses fuel volumes. For an electric car, multiply the trip distance by its energy use (kWh per mile or per 100 km) and by your electricity or charging price.
Sources
- Fuel Economy Information - US Department of Energy and US Environmental Protection Agency, fueleconomy.gov
- Unit Conversion - National Institute of Standards and Technology (NIST)