How this calculator works
We convert your distance to miles if needed, convert your efficiency figure to UK miles per gallon if it was entered as litres per 100km, then work out how many gallons (and litres) of fuel the journey would use using the correct UK imperial gallon of 4.54609 litres. Multiplying the litres used by your fuel price per litre gives the total cost, which we then divide by the number of miles and the number of people if you're splitting the cost.
The only figure worth double-checking is your fuel efficiency. The number on a car's spec sheet (the "combined" WLTP figure) is measured under fairly gentle test conditions and tends to run 10-20% better than what most drivers actually get, especially on shorter urban trips or in cold weather. If you know your actual average from filling up, use that instead — it'll give you a far more honest number.
Typical UK fuel efficiency by vehicle type
| Vehicle type | Typical real-world MPG (UK) |
|---|---|
| Small petrol hatchback | 45–55 mpg |
| Small diesel hatchback | 55–65 mpg |
| Mid-size petrol saloon/estate | 38–48 mpg |
| Petrol SUV/crossover | 32–42 mpg |
| Diesel SUV | 42–50 mpg |
| Hybrid hatchback | 55–70 mpg |
These are rough real-world ranges gathered from typical UK owner-reported figures, not manufacturer claims — useful as a sense check if you're not sure what to put in.
Frequently asked questions
Why does this use UK gallons and not US gallons?
A UK (imperial) gallon is 4.54609 litres, while a US gallon is only 3.78541 litres — about 20% smaller. Plenty of fuel calculators built for a US audience use the US gallon by default, which quietly makes every result about 20% wrong for anyone filling up in the UK. This calculator always uses the UK gallon.
Where do I find my car's real fuel efficiency?
The most reliable way is to reset your trip computer at a full tank, drive normally until your next fill-up, and divide the miles covered by the litres needed to fill back up (converted to gallons). Do this over a few tanks and average it — that beats any spec-sheet number.
Does this include the cost of tolls, parking or congestion charges?
No — this calculator is fuel only. If you regularly hit toll roads, the Dartford Crossing, or a congestion or clean air zone charge, add those on separately.
How accurate is the pence-per-litre price I should use?
Use whatever you actually paid at your usual filling station, or a current national average if you're planning ahead — UK fuel prices are published regularly by the RAC Fuel Watch and similar trackers, and vary a fair amount by region and by supermarket versus branded forecourts.
Can I use this for a round trip?
Yes — just enter the full round-trip distance rather than the one-way distance, or use the Fuel Split Calculator, which has a dedicated round-trip toggle.