Fuel Cost Calculator
Work out what a journey will cost in fuel from the distance, your car's fuel economy and the price at the pump. Enter the trip in miles, your miles per gallon and the price per litre to see the litres needed and the total cost, with an optional split between passengers.
Inputs
Results
Litres = miles divided by mpg, times 4.54609 litres per imperial gallon. Total cost = litres times the pump price per litre.
The link saves your inputs so you can bookmark or share this exact result.
How the journey fuel cost is worked out
This calculator estimates what a car journey costs in fuel from three numbers you already know: the distance in miles, your car's fuel economy in miles per gallon, and the pump price per litre. It bridges the awkward UK mismatch where economy is quoted in miles per imperial gallon but fuel is sold by the litre, converting at 4.54609 litres per gallon.
The result shows the litres the trip will burn, the total cost, and the cost per mile, which is the most useful number for comparing routes or deciding whether a detour to a cheaper supermarket forecourt is worth it. An optional split divides the total between passengers for shared journeys and car pools.
Because fuel economy in the real world depends on speed, load, tyres and temperature, the figure is an estimate. Using the long-term average mpg from your car's trip computer rather than the official brochure figure makes it a realistic one.
How to use the fuel cost calculator
- Enter the journey distance in miles. For a return trip, double the one-way distance.
- Enter your car's real-world fuel economy in miles per gallon.
- Enter the current fuel price per litre, for example 1.40.
- Set how many people are splitting the cost if you are sharing, and read the total, litres and per-mile figures.
Worked examples
A 200 mile trip at 45 mpg with fuel at 1.40 per litre
Inputs: Distance 200 miles, economy 45 mpg, price 1.40 per litre, 1 person.
Result: About 20.2 litres of fuel costing roughly 28.29 in total, which is about 14p per mile.
The same trip shared between four people
Inputs: As above with 4 people splitting the cost.
Result: The total stays about 28.29 but each person pays roughly 7.07, which is the figure to use when settling up after a shared drive.
Limitations and common mistakes
Edge cases and limitations
- Miles per gallon uses the imperial gallon of 4.54609 litres, not the smaller US gallon, so US mpg figures will overstate economy here by about 20 percent.
- Real economy varies with driving style, speed, load and weather; motorway mpg and urban mpg for the same car can differ by a third.
- The result covers fuel only. Wear, depreciation and tolls are not included, so the full cost of motoring per mile is higher.
- Electric cars do not fit the mpg model; their equivalent is pence per mile from kWh used, which this calculator does not cover.
Common mistakes
- Using the official combined mpg figure, which is measured in laboratory conditions. Knock off roughly 15 percent or use your dashboard average for a realistic cost.
- Entering the price in pence rather than pounds per litre. A price of 140 instead of 1.40 makes the trip look one hundred times more expensive.
- Forgetting to double the distance for a return journey.
Frequently asked questions
How do I calculate the fuel cost of a journey?
Divide the distance by your car's miles per gallon to get gallons used, convert to litres by multiplying by 4.546, then multiply by the price per litre. For a 200 mile trip at 45 mpg and 1.40 per litre that is 4.44 gallons, about 20.2 litres, costing roughly 28.30.
Why does the calculator use mpg with a price per litre?
Because that mismatch is how fuel is actually sold and quoted in the UK: car economy figures are published in miles per imperial gallon while pumps price in litres. The calculator does the gallon to litre conversion for you using 4.54609 litres per imperial gallon.
What mpg figure should I use for my car?
Real-world economy is usually 10 to 20 percent worse than the official figure, especially for short urban trips. If your car shows a long-term average mpg on the dashboard, use that. Otherwise take the official combined figure and knock off about 15 percent for a realistic estimate.
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