How to use the fuel cost calculator
- Enter the trip distance in miles or kilometres. Tick round trip to double it.
- Choose the fuel economy unit you know — US mpg, UK mpg, L/100 km or km/L — and enter the figure.
- Enter the fuel price and whether it is per US gallon, per litre or per UK gallon.
- To share costs, enter how many people are splitting the fuel bill.
The formulas
US / UK mpg: Gallons = Miles ÷ mpg L/100 km: Litres = Kilometres × L/100 km ÷ 100 km/L: Litres = Kilometres ÷ km/L Fuel cost = Fuel used × Price per gallon (or litre) Cost per mile = Price per gallon ÷ mpg
Worked examples
- US road trip: 300 miles at 25 mpg = 12 gallons × $3.50 = $42. A round trip costs $84, or $42 each for two people.
- Europe: 500 km at 6.5 L/100 km = 32.5 L × €1.80 = €58.50.
- UK: 200 miles at 45 mpg (UK) = 4.44 UK gallons = 20.2 L × £1.45 = £29.30.
Fuel economy conversion table
| mpg (US) | mpg (UK) | L/100 km | km/L |
|---|---|---|---|
| 15 | 18.0 | 15.7 | 6.4 |
| 20 | 24.0 | 11.8 | 8.5 |
| 25 | 30.0 | 9.4 | 10.6 |
| 30 | 36.0 | 7.8 | 12.8 |
| 35 | 42.0 | 6.7 | 14.9 |
| 40 | 48.0 | 5.9 | 17.0 |
| 50 | 60.0 | 4.7 | 21.3 |
Cost per 100 miles at different gas prices
| Fuel economy | $3.00/gal | $3.50/gal | $4.00/gal | $5.00/gal |
|---|---|---|---|---|
| 20 mpg | $15.00 | $17.50 | $20.00 | $25.00 |
| 25 mpg | $12.00 | $14.00 | $16.00 | $20.00 |
| 30 mpg | $10.00 | $11.67 | $13.33 | $16.67 |
| 40 mpg | $7.50 | $8.75 | $10.00 | $12.50 |
Getting an accurate estimate
- Use your real mpg: fill the tank, reset the trip meter, drive normally, then divide the miles by the gallons needed to refill. Window-sticker figures are often optimistic.
- Highway vs city: most cars use less fuel per mile on the highway, but very high speeds increase drag sharply.
- Towing and loads: a trailer or heavy roof load can cut fuel economy by 10–30% or more.
- Prices vary on the route: fuel is often cheaper away from highway service areas and in some states or countries than others.
- Compare with electric: use the EV charging cost calculator to compare the same trip in an electric car.
Budgeting for a longer trip
For a multi-day road trip, add up the planned driving for each day and add 10–15% for detours, side trips and searching for parking. In a rental car, check whether you must return it full: refuelling charges at the rental desk are often far higher than pump prices. If several people share the car, splitting fuel evenly is the simplest fair method; for one-way passengers, split the cost of the legs they ride along for.