The cost per mile formula
Cost per mile = (4.546 ÷ MPG) × fuel price per litre
4.546 is the number of litres in a UK gallon. Dividing it by your MPG gives litres used per mile; multiplying by the price gives pence per mile.
Cost per mile at £1.45 a litre
- 30 MPG: 22.0p per mile
- 40 MPG: 16.5p per mile
- 50 MPG: 13.2p per mile
- 60 MPG: 11.0p per mile
Why cost per mile is useful
Once you know your cost per mile you can price any trip mentally, compare two cars fairly, or check whether a mileage allowance covers your fuel. For a full journey breakdown use the fuel cost calculator.
Fuel cost vs the total cost of driving
The cost of driving per mile is higher than the fuel figure alone. Insurance, road tax, servicing, tyres and depreciation all add to it — but fuel is the part that changes most directly with how far you drive.
Petrol vs diesel fuel costs
Diesel usually costs a little more per litre than petrol, but diesel cars typically achieve better fuel economy, especially on longer motorway runs. Whether diesel works out cheaper per mile depends on the specific cars being compared, the prices you pay and how you drive.
Neither fuel is always cheaper. The fairest comparison is cost per mile: use the petrol cost per mile and diesel cost per mile calculators with your own figures.