Running costs
Fuel cost calculator
Enter the distance and fuel economy; the pump price starts at this week's UK average.
How much does fuel cost for a journey?
In the UK, this calculator starts with the DESNZ average unleaded price of 161.61p a litre for the week commencing 31 August 2026. Miles divided by mpg gives gallons; multiplying by 4.54609 gives litres, then the pump price gives the journey cost.
161.61p
183.49p
4.54609
Checked on 31 August 2026.Department for Energy Security and Net Zero, Weekly road fuel prices (as of 31 August 2026)
Real world fuel economy by segment
| Segment | Petrol mpg | Diesel mpg | 100 miles, petrol |
|---|---|---|---|
| City car | 48.9 | 55.3 | £15.02 |
| Supermini | 45.1 | 62.2 | £16.29 |
| Family hatchback | 43.4 | 54.7 | £16.93 |
| Estate | 42.2 | 53.6 | £17.41 |
| Medium SUV | 38.8 | 53.5 | £18.94 |
| Large SUV | 35.6 | 45.4 | £20.64 |
| Executive saloon | 40.9 | 52.2 | £17.96 |
Four things that cost more fuel than you think
- A roof box or roof bars. The drag penalty is worst at motorway speed, which is exactly where most long journeys are.
- Short cold journeys. An engine below its operating temperature is far less efficient, so a two mile trip can be double the average.
- Tyre pressure. Underinflated tyres cost fuel continuously and nobody notices, because nothing about the car feels different.
- Speed. The energy needed to push a car through the air rises with the square of speed, so 80 mph costs a great deal more than 70 for very little time saved.
Common questions
- How do I work out fuel cost for a journey?
- Divide the miles by the car's miles per gallon to get gallons, multiply by 4.54609 to get litres, then multiply by the pump price in pence and divide by 100. The result shows each stage of the calculation.
- Which gallon is a UK mpg figure measured in?
- The imperial gallon of 4.54609 litres. The US gallon is 3.785 litres, so a calculator using it understates a UK tank by a fifth. That is the commonest error in an online fuel cost tool.
- Why does my car never match its official economy?
- Because the official figure comes from a laboratory cycle. Real world economy is typically 5 to 20 per cent worse depending on the segment, and small turbocharged engines in tall cars have the widest gap of all.
- Should I use miles per gallon or litres per 100km?
- Whichever your car reports. They are reciprocals of each other, so a calculator that treats them as a simple ratio drifts further from the truth the further you get from a mid range figure. This one converts through the reciprocal.
Sources
- Department for Energy Security and Net Zero, Weekly road fuel prices (as of 31 August 2026)
- Ofgem, Energy price cap unit rates and standing charges (as of 1 July 2026)
- Honest John, Real MPG: Hyundai i10 (2019 on) (as of 30 July 2026)
- Honest John, Real MPG: Fiat 500 (2008 to 2025) (as of 30 July 2026)
- Honest John, Real MPG: Ford Fiesta (2017 to 2023) (as of 30 July 2026)
- Honest John, Real MPG: Ford Focus (2018 to 2025) (as of 30 July 2026)