Fuel cost calculator
This calculator turns a distance, a miles-per-gallon figure and a pump price per litre into a fuel cost and a cost per mile, converting gallons to litres at the imperial-gallon rate. For example, 10,000 miles at 50 MPG and 140p a litre costs an estimated £1,273, or 12.7p a mile. No statutory fuel duty rate applies here.
Why does cost per mile matter more than the total fuel bill?
A total fuel bill only means something next to the miles it buys. Cost per mile strips that out, so a longer commute, a work trip that might be reclaimed, or a less economical car can be weighed against a more frugal one on the same footing.
The calculation itself is simple: distance divided by MPG gives gallons, converted to litres, then multiplied by the pump price. The one trap is the gallon, since UK economy figures use the imperial gallon of 4.54609 litres rather than the smaller US gallon, and mixing them up overstates the cost by about a fifth.
What does the worked example show?
Take 10,000 miles a year in a car doing 50 MPG, with fuel at 140p a litre. That is 200 imperial gallons, or 909 litres, which at 140p comes to £1,273 for the year. Per mile that is 12.7p, or £0.13. Drop the economy to 40 MPG and the same year costs more, which is why the MPG box is worth getting right.
Common questions
How is the fuel cost worked out?
The distance is divided by your miles per gallon to get gallons used, converted to litres at 4.54609 litres per imperial gallon, then multiplied by the pump price. UK MPG always uses the imperial gallon, which is larger than the US gallon, so the conversion matters.
Should I enter a journey or my annual mileage?
Either works. Enter a single trip distance for the cost of that journey, or your yearly mileage for an annual fuel bill. The cost per mile is the same figure in both cases.
What MPG should I use?
Use your own observed figure if you track it, because real driving is usually below the official number. If you only have the manufacturer figure, expect real-world economy to come in roughly 10 to 20 per cent lower, more in cold weather or heavy town driving.
Do I enter the price in pounds or pence?
Enter the price per litre in pence, the way it is shown on the forecourt, so 139.9 is entered as about 140. The tool converts to pounds for the total.
Does this include an electric car?
No. This is for petrol and diesel, priced per litre. For charging costs per mile and a side-by-side with petrol, use the EV vs petrol running cost calculator.
Why does cost per mile matter more than the total fuel bill?
A total fuel bill only means something next to the miles it buys, so two drivers with very different mileages cannot compare their bills directly. Cost per mile removes that variable, making it possible to weigh a longer commute, a work trip, or a less economical car against a more frugal one on the same footing. It is also the figure that lines up against an electric car or a mileage allowance rate.
What does the worked example show?
Take 10,000 miles a year in a car doing 50 MPG, with fuel at 140p a litre. That comes to 200 imperial gallons, or 909 litres, giving an estimated fuel cost of £1,273 for the year, equal to 12.7p a mile. Dropping the MPG figure raises both totals, which is why an accurate MPG matters as much as the pump price.
Sources & Rate Verification
Rates verified against official statutory guidance on 6 September 2026.