Petrol Cost Per Mile Calculator
Find out exactly what each mile costs you in fuel. Enter your car's MPG and the pump price and we'll do the gallon-to-litre maths — using the UK gallon (4.546 litres) — to give you a precise pence-per-mile figure.
Cost per mile calculator
UK gallon = 4.546 litres.
Cost per mile = (price/litre × 4.54609) ÷ MPG. Real-world MPG is often below the official figure.
How to work out cost per mile
Cost per mile is the single most useful number for any driver. It folds your car's efficiency and the fuel price into one figure you can compare across cars and journeys. The formula is simple once you handle the gallon: cost per mile = (price per litre × 4.54609) ÷ MPG. The 4.54609 turns the UK gallon — which your MPG is measured in — into litres.
At 140.9p a litre and 45 MPG, each mile costs about 14.2p. Over a 100-mile journey that's around £14.20 in fuel. A car returning 30 MPG at the same price costs about 21.3p a mile.
Cost per mile at a glance
| MPG | At 135p/litre | At 145p/litre |
|---|---|---|
| 25 MPG | 24.5p | 26.4p |
| 35 MPG | 17.5p | 18.8p |
| 45 MPG | 13.6p | 14.6p |
| 55 MPG | 11.2p | 12.0p |
| 65 MPG | 9.4p | 10.1p |
Petrol vs electric per mile
Cost per mile is also how petrol and electric cars are fairly compared. A petrol car typically costs 13–17p a mile; an electric car charged at home off-peak can be 3–6p a mile, though public rapid charging narrows the gap considerably. Our EV charging cost calculator works out the electric side.
Use real-world MPG. The official figure on the brochure is measured in a lab and is often 10–20% optimistic. Track a few tankfuls to find your true MPG, then your cost per mile will be accurate.
From cost per mile to a full journey
Once you know your pence per mile, multiplying by the distance gives the fuel cost of any trip. For return journeys, MPG tweaks and a tidy total, the fuel cost calculator does the same sums for a whole journey. The latest UK pump prices are published weekly by the Department for Energy Security and Net Zero.
Frequently asked questions
How do I work out cost per mile for petrol?
Cost per mile = (price per litre × 4.54609) ÷ MPG. The 4.54609 converts the UK gallon to litres. At 140p a litre and 45 MPG that's about 14.1p per mile.
What is a typical cost per mile in the UK?
For a petrol car doing 40–50 MPG at current prices, fuel is roughly 13–17p per mile. A thirsty car at 25 MPG can top 25p, while an efficient diesel can be under 12p.
Does this use the UK or US gallon?
The UK imperial gallon of 4.54609 litres, which is what UK MPG figures are based on. Using the smaller US gallon would understate cost per mile by about 20%.
Why is cost per mile useful?
It's the fairest way to compare cars and trips. Commuting decisions and the choice between two cars come down to pence per mile, because it folds in the fuel price as well as MPG.
How does cost per mile compare to an electric car?
An electric car charged at home off-peak can cost around 3–6p per mile, below petrol's 13–17p. Public rapid charging costs more, sometimes approaching petrol levels.