United Kingdom
Fuel cost calculator
Before a long drive it helps to know what the fuel will cost. Give this the trip distance, your car's consumption in litres per 100 km, and the current price per litre, and it returns the litres you will burn and the total spend. It suits budgeting a road trip, deciding whether driving beats the train, or working out a fair share when several people travel together. The same method covers a daily commute or a one-off holiday run, and a quick toggle handles return journeys.
Economy is in UK miles per gallon. Fuel is priced per litre, the usual pump unit.
How it works
- Litres used equals the distance divided by 100, multiplied by your litres-per-100-km rating. A 250 km trip at 6 L/100km burns 15 litres.
- The cost is that litre figure multiplied by the price you pay per litre.
- For a there-and-back journey, double the one-way distance before reading the result.
- Lower consumption (a smaller L/100km number) or a cheaper pump price both reduce the total, in direct proportion.
cost = (distance / 100) x consumption x price
Two steps sit behind the number. First the litres burned: divide the distance by 100 and multiply by the rated litres per 100 km, since consumption is quoted against that 100 km yardstick. Then multiply those litres by the pump price to get the spend. Distance, consumption and price each enter as a straight multiplier, so doubling any one of them doubles the bill.
- distance
- trip length in kilometres, doubled for a return journey
- consumption
- fuel use in litres per 100 km, from the trip computer or a manual tank-to-tank check
- price
- pump price paid per litre
Typical petrol and diesel consumption
| Small petrol hatchback | 5 to 6 L/100km | gentle mixed driving |
| Mid-size diesel saloon or estate | 5 to 7 L/100km | steady on the motorway |
| Family petrol SUV | 8 to 10 L/100km | heavier and less aerodynamic |
| Large van or 4x4 | 10 to 14 L/100km | loaded, or towing |
Worked example
A 100 km drive at 7 litres per 100 km, fuel at 1.50 per litre uses 7 litres and costs 10.50. Make it a 500 km trip in a thirstier vehicle at 9 L/100km and 1.80 per litre, and the bill is 45 litres for 81.00.
Key facts
- Consumption is rated per 100 km, so a 50 km trip uses half the litre figure on the label.
- Cost scales in a straight line with all three inputs, with no fixed standing charge added.
- The same sum works for petrol or diesel because only the price per litre and the consumption rate change.
- Quoting in litres per 100 km means a lower number is more efficient, the reverse of miles per gallon.
Tips
- Steady speeds around 90 to 110 km/h on the motorway usually return the lowest consumption; hard acceleration and high speed both lift it sharply.
- A roof box or roof bars add drag worth roughly one extra litre per 100 km at motorway pace, so take them off when not needed.
- Check tyre pressures before a long run, as soft tyres quietly raise rolling resistance and fuel use.
- For an honest figure, measure your own consumption tank to tank rather than trusting the official combined number, which most cars beat only in light traffic.
Fuel cost by distance, consumption and price (one way)
| Distance (km) | Consumption (L/100km) | Price per litre | Litres | Cost |
|---|---|---|---|---|
| 100 | 6 | 1.5 | 6 | 9 |
| 300 | 6 | 1.5 | 18 | 27 |
| 500 | 6 | 1.5 | 30 | 45 |
| 500 | 8 | 1.5 | 40 | 60 |
| 500 | 8 | 1.8 | 40 | 72 |
Frequently asked questions
My car shows miles per gallon, not litres per 100 km.+
For UK gallons, divide 282.5 by your mpg to get litres per 100 km. So 40 mpg is about 7.1 L/100km. US gallons are smaller, so use 235.2 instead of 282.5.
Are tolls, parking and wear included?+
No. The figure is fuel alone. Road tolls, parking, vehicle wear and any congestion charges need adding on top for a true trip budget.
Where do I find my consumption figure?+
Most cars show average litres per 100 km on the trip computer. Otherwise, fill the tank, drive a known distance, refill, and divide litres added by distance to get your real-world rate.
Will the real cost match this exactly?+
Rarely to the penny. Motorway speed, a full load, cold weather, hills and heavy traffic all push consumption above the official figure, so treat the result as a close estimate.
Things to watch
- Treat the result as an estimate. Cold starts, hills, headwinds, a full load and stop-start traffic all push real consumption above the rated figure.
- Pump prices move week to week and differ between motorway services and supermarket forecourts, so a quote can be out of date by the time you fill up.
- For a return trip, double the one-way distance first, or the cost shown will be only half of what the journey actually takes.
Last updated: 2026-01-01
This is an estimate for general guidance, not financial, tax, legal or medical advice. Figures can change and individual circumstances vary. Always confirm with the official sources listed before making decisions.
- Fuel only; excludes tolls, parking, servicing and depreciation.
- Real consumption varies with speed, load, terrain, weather and driving style.
- Electric vehicles use kWh rather than litres, so this petrol and diesel tool does not apply to them.
Reviewed by Vikas Dulgunde.