How to use the fuel cost calculator
- Enter the trip distance and choose miles or kilometres. Tick Return trip to double it.
- Enter your vehicle’s fuel economy and choose the matching unit. Check whether an MPG figure is US or imperial.
- Enter the fuel price you expect to pay and whether it is per litre, per US gallon or per imperial gallon.
- Optionally add travellers, tolls, parking, a currency label and a second vehicle to compare.
Changing a unit converts the number in that box so it still describes the same distance, economy or price. Switching back restores your original entry exactly.
Worked example
Sample figures for illustration only, not a current fuel price: a 300-mile trip in a car that returns 30 MPG (US), with fuel at 3.50 per US gallon.
- Fuel needed: 300 ÷ 30 = 10.0 US gallons (37.9 litres).
- Fuel cost: 10.0 × 3.50 = 35.00, or 0.117 per mile.
Now suppose the 30 MPG figure was really imperial. Thirty miles per imperial gallon means 30 miles from 4.546 litres rather than 3.785 litres, so the car is less efficient than the US figure suggests. The trip would need 45.5 litres instead of 37.9, and at the same price per US gallon would cost 42.03 instead of 35.00. Choosing the wrong gallon is a 20% error.
US gallons and imperial gallons
The US gallon is defined as 231 cubic inches, exactly 3.785411784 litres (NIST Handbook 44, Appendix C). The imperial gallon is exactly 4.54609 litres (UK Weights and Measures Act 1985, Schedule 1). Because the imperial gallon is about 20.1% larger, the same car shows a higher MPG figure in imperial units.
| L/100 km | km/L | MPG (US) | MPG (imperial) |
|---|---|---|---|
| 4.0 | 25.0 | 58.8 | 70.6 |
| 5.0 | 20.0 | 47.0 | 56.5 |
| 6.0 | 16.7 | 39.2 | 47.1 |
| 7.0 | 14.3 | 33.6 | 40.4 |
| 8.0 | 12.5 | 29.4 | 35.3 |
| 10.0 | 10.0 | 23.5 | 28.2 |
| 12.0 | 8.3 | 19.6 | 23.5 |
| 15.0 | 6.7 | 15.7 | 18.8 |
Check: 7.84 L/100 km equals 30 MPG (US).
Formulas used
fuel (L) = distance (km) × consumption (L/100 km) ÷ 100
L/100 km = 235.2146 ÷ MPG (US) = 282.4809 ÷ MPG (imperial) = 100 ÷ km/L
fuel cost = fuel (L) × price per litre
total cost = fuel cost + tolls + parking
cost per person = total cost ÷ travellers All inputs are converted to kilometres, litres per 100 km and price per litre before calculating, using 1 mile = 1.609344 km exactly. Results are rounded only for display.
Limitations
- Results depend entirely on the fuel economy and price you enter.
- Real consumption varies with driving style, speed, traffic, terrain, weather, load and vehicle condition.
- The currency is a label; there is no exchange-rate conversion and no live price data.
- This is a trip fuel estimate, not a complete cost of vehicle ownership.
Frequently asked questions
What is the difference between US and imperial MPG?
They use different gallons. A US gallon is exactly 3.785411784 litres; an imperial gallon, used in the UK, is exactly 4.54609 litres, about 20% larger. So 30 MPG (imperial) is less efficient than 30 MPG (US): it equals about 25 MPG (US). Always choose the gallon that matches where your figure came from.
Does this convert currencies or use live fuel prices?
No. The currency box is only a label for the results, and you enter the fuel price yourself. Nothing is converted between currencies and no prices are fetched.
Why is my real fuel cost different?
The estimate is only as good as the fuel economy you enter. Real consumption changes with speed, traffic, terrain, weather, load, air conditioning, tyre pressure and vehicle condition. Official ratings often differ from real-world figures.
Is this the full cost of running a car?
No. It covers fuel plus any tolls and parking you enter. It does not include depreciation, insurance, maintenance, tyres, finance or tax.
Can I use it for an electric vehicle?
Not directly. The calculator works with liquid fuel volumes. Electric vehicles are measured in energy (kWh) rather than litres or gallons.
How is the cost per person worked out?
The total of fuel, tolls and parking is divided equally by the number of travellers you enter. It is a simple equal split, not a recommendation for how to share costs.
Last updated .