Fuel Cost Calculator
Work out what a trip costs in fuel, and split it between passengers.
Trip type
Fuel cost for this trip
666.67
Fuel needed
6.67 litres
Cost per km
6.67
Total distance
100 km
Work out what a trip will cost in fuel based on distance, your vehicle's fuel economy, and the local fuel price — then split that cost evenly between passengers for a road trip or carpool.
Supports both distance-per-volume and volume-per-distance fuel economy conventions, so it works whether you think in miles-per-gallon or litres-per-100km.
MPG and L/100km run in opposite directions
Higher MPG is better; lower L/100km is better. They are reciprocals of each other, which means improvements are not evenly spaced — and that has a genuinely counter-intuitive consequence.
Going from 15 to 20 MPG saves more fuel over the same distance than going from 40 to 50 MPG, even though the second looks like a bigger jump. Over 10,000 miles the first change saves about 167 gallons and the second about 50. If you run two vehicles, improving the thirstier one is where the money is.
| MPG (US) | L/100km | Fuel for 500 km |
|---|---|---|
| 15 | 15.7 | 78.4 L |
| 25 | 9.4 | 47.0 L |
| 35 | 6.7 | 33.6 L |
| 50 | 4.7 | 23.5 L |
Why real economy falls short of the sticker figure
- Official figures come from standardised test cycles gentler than real driving. Expect 10–20% worse in practice.
- Short trips are disproportionately expensive — a cold engine can use nearly double the fuel for the first few kilometres.
- Highway speed matters more than people think: aerodynamic drag rises with the square of speed, so 120 km/h can cost 20% more fuel than 100 km/h over the same distance.
- Roof boxes and roof racks add meaningful drag even when empty. Take them off when not in use.
- Under-inflated tyres, air conditioning and a heavily loaded vehicle each add a few percent.
- For a realistic figure, track your own economy over a few full tanks rather than using the manufacturer's number.
Frequently asked questions
- What if my car's fuel economy is in L/100km, not MPG?
- Switch the unit toggle — the calculator accepts either convention and converts internally.
- How do I split the cost between passengers fairly?
- Enter the number of people sharing the trip and the tool divides the total fuel cost evenly across them.
- Does this account for a round trip?
- Enter the round-trip distance directly, or double a one-way distance before calculating.
- Is a UK gallon the same as a US gallon?
- No. An imperial gallon is about 4.55 litres and a US gallon about 3.79, so UK MPG figures look roughly 20% better for the same real economy. Check which convention your figure uses.
- Should I use the manufacturer's MPG figure?
- Only as a starting point. Real-world economy is typically 10–20% worse. Filling up, resetting the trip meter and dividing distance by fuel used over a couple of tanks gives a far more accurate number.