UK Calculator Platform
Automotive & TravelRunning Cost

Fuel Cost Calculator

Inputs

Results

Enter values and calculate to see results.

Related Calculators

Fuel Economy Calculator

Automotive & TravelRunning Cost

Mileage Calculator

Automotive & TravelRunning Cost

Vehicle Depreciation Calculator

Automotive & TravelRunning Cost

Car Loan Calculator

Automotive & TravelVehicle Finance

Disclaimer: Vehicle cost, fuel consumption, EV charging and depreciation figures are estimated models based on entered parameters and standard UK averages. Real-world performance varies with vehicle condition, driving behaviour, payload and ambient temperatures.

What a journey costs in fuel

UK fuel economy is quoted in miles per gallon but fuel is sold in litres, so costing a journey means converting between the two. An imperial gallon is 4.54609 litres.

What this calculator does

  • Works out the fuel used and the cost for a journey of a given distance.
  • Handles the miles-per-gallon to litres conversion.
  • Multiplies up for repeated trips, such as a commute.

How the calculation works

The awkward part of costing a UK journey is that the two units do not match: economy is quoted in miles per imperial gallon, while fuel is priced in pence per litre. The calculation divides the total distance by the fuel economy to give gallons used, converts those to litres using the imperial gallon of 4.54609 litres, and multiplies by the price. The imperial gallon matters here — a US gallon is about 3.785 litres, and using it would understate consumption by around 17%, which is a large error on a long journey. Multiplying by the number of trips turns a single journey into a commute or a regular run, which is usually the more useful figure. The arithmetic itself is straightforward; the accuracy depends almost entirely on whether the miles-per-gallon figure you enter reflects the driving you actually do.

The rule

Litres = (distance in miles ÷ miles per gallon) × 4.54609. Cost = litres × price per litre.

Step by step

  1. Multiply the trip distance by the number of trips to give total miles.
  2. Divide by the fuel economy in miles per imperial gallon to give gallons used.
  3. Multiply by 4.54609 to convert gallons to litres.
  4. Multiply by the price per litre to give the cost.

Worked example

A 240-mile journey made twice, in a car returning 45 mpg, with fuel at 148p a litre.

What was entered

Inputs used in the worked example
Trip distance240 miles
Fuel economy45 UK MPG
Fuel price148p per litre
Number of trips2

The arithmetic

  1. Two trips of 240 miles is 480 miles in total.
  2. At 45 mpg that is 480 ÷ 45 = 10.67 imperial gallons.
  3. Converting at 4.54609 litres per gallon gives 48.49 litres.
  4. At 148p a litre the fuel cost is £71.77.
  5. That works out at about 15p a mile — a figure worth knowing before agreeing to share costs.

What the calculator returns

Results produced by the worked example
Fuel used (litres)48.492
Fuel cost£71.77

Key assumptions

  • The economy figure is in miles per imperial gallon, not US gallons.
  • The same economy is achieved for the whole journey.
  • The fuel price is the price actually paid per litre.

Limitations

  • Real-world fuel economy is usually below the official figure, and varies a great deal with speed, load, traffic, weather, tyre pressure and driving style. Motorway cruising and urban stop-start driving can differ by a third or more.
  • This covers fuel only. It is not the cost of running the vehicle, which also includes depreciation, insurance, tax, servicing and tyres.
  • Fuel prices vary noticeably between forecourts and regions, and motorway services are typically the most expensive option.
  • Electric vehicles are not covered, since their running costs are worked out from kilowatt-hours and a tariff rather than from litres.
  • Tolls, congestion and clean air zone charges and parking are not included.

Common questions

Is a gallon here the same as a US gallon?
No, and the difference is large. A UK imperial gallon is 4.54609 litres against about 3.785 for a US gallon. Using the US figure would understate fuel used by roughly 17%, which is a substantial error on a long journey.
Why does my real economy fall short of the official figure?
Official figures come from standardised test conditions that no real journey matches. Speed, traffic, load, weather, tyre pressure and driving style all reduce economy, and short cold-start journeys are particularly costly.
Is this the full cost of the journey?
No — it is fuel only. Depreciation, insurance, tax, servicing and tyres all accrue with mileage too, and per-mile running cost is typically well above the fuel cost alone.
Can I use this for an electric car?
No. Electric running costs are worked out from kilowatt-hours consumed and the tariff you charge at, which is a different calculation with very different numbers.

Related calculators

Official sources

Every figure in this guide was checked against the sources below. Where a source could not confirm a figure, it is marked as requiring verification rather than presented as settled.