This is our full fuel cost calculator. It handles one-way and return trips, miles or kilometres, UK MPG or L/100km, and repeat journeys — so it works equally well for a one-off visit to family or a regular school run.
How does a fuel cost calculator work?
The calculator first works out how much fuel your journey needs, then multiplies that by the price you pay per litre:
Fuel cost = fuel required (litres) × fuel price per litre
Fuel required comes from your distance and your car's fuel economy. Because UK fuel economy is quoted in miles per imperial gallon and fuel is sold in litres, we convert using 1 UK gallon = 4.546 litres:
Litres = (miles ÷ MPG) × 4.546
For example, 100 miles in a car averaging 40 MPG uses 2.5 gallons, or about 11.4 litres. At £1.45 a litre that's roughly £16.48.
Getting the most accurate estimate
- Use real-world MPG. Official figures are measured in lab conditions; your trip computer average is usually more realistic.
- Use today's price. Check the price at your usual forecourt rather than a national average.
- Think about the route. Motorway cruising and stop-start town traffic give very different MPG.
What is UK MPG?
UK MPG measures how many miles a car travels on one imperial gallon of fuel — 4.546 litres. A US gallon is smaller, at 3.785 litres, so the same car shows a lower MPG figure in US units. A car returning 50 MPG in the UK would read about 41.6 MPG in US terms.
That matters if you're using figures from American websites or reviews: putting a US MPG number into a UK calculator will overstate your fuel cost. Everything on this site uses UK imperial MPG unless you switch to L/100km.
How can I reduce my fuel costs?
Small habits add up over a year of driving. None of these are dramatic on their own, but together they can noticeably improve your real-world MPG:
- Accelerate and brake smoothly. Reading the road ahead and avoiding harsh acceleration uses less fuel.
- Keep tyres at the correct pressure. Under-inflated tyres increase rolling resistance. Check the pressures in your handbook or on the door pillar.
- Remove unnecessary weight. Clear out the boot and take off empty roof boxes and bars when you don't need them.
- Plan journeys and combine trips. A warm engine is more efficient, so one longer round trip often beats several short ones.
- Keep the car maintained. Regular servicing keeps the engine running as intended.
- Compare fuel prices. Prices can vary between nearby forecourts, and motorway services are often more expensive.
Need something more focused? Try the petrol or diesel calculators, or the commute calculator for regular trips.