Free calculator
Fuel cost calculator
Enter the distance, your car's mpg and the price per litre, and see what the journey costs in fuel. Prefilled with today's typical UK price.
Prices prefilled from the official Fuel Finder data, updated 28 August 2026. Change any box and the answer updates as you type.
How the fuel cost is worked out
The sum is simple. Your miles divided by your mpg gives gallons, gallons times 4.546 gives litres, and litres times the price per litre gives the cost. The price box is prefilled with today's typical UK petrol price from the official data, so change it to the price at the forecourt you actually use, or to the diesel price if you drive a diesel.
The mpg figure matters more than people think. The number in the brochure is usually optimistic, so if you want an honest answer use the figure your car actually returns in normal driving, which our mpg calculator will work out from a tank of fuel.
Cutting the number
There are two ways to shrink what a journey costs. One is to use less fuel, by driving smoothly and keeping the speed down, which our guide on how to use less fuel covers. The other, which usually saves more, is to pay less per litre by filling up at the right forecourt. Put your postcode into the price finder to see the cheapest within five miles.
Common questions
How do I calculate the fuel cost of a journey?
Divide the miles by your mpg to get gallons, multiply by 4.546 to get litres, then multiply by the price per litre. For example 100 miles at 45 mpg is about 10.1 litres, which at 162p a litre costs about 16 pounds.
What mpg should I use?
Use the mpg your car actually returns in everyday driving rather than the brochure figure, which is usually optimistic. You can work out your real mpg from one full tank using the mpg calculator on this site.
Is the price prefilled accurate?
It is today's typical UK price from the official Fuel Finder data, refreshed twice a day. Your local forecourt may be cheaper or dearer, so for an exact answer enter the price you actually pay.