UK Fuel Cost Calculator

How to use the fuel cost calculator

Enter the distance of your journey (in miles or kilometres), your car's fuel efficiency (in MPG or litres per 100km), and the price you're paying per litre at the pump. The calculator works out the total litres you'll use, the total cost, and your cost per mile and per kilometre — handy for budgeting a road trip, comparing cars, or working out a fair fuel contribution to split with passengers.

Fuel remains one of the biggest variable costs of running a car in the UK, and prices can shift noticeably from month to month and forecourt to forecourt. Knowing your actual cost per mile makes it much easier to budget for regular commutes, compare the running costs of different vehicles, or simply check whether a long trip is worth taking by car versus train or plane.

The maths behind the numbers

If you enter your efficiency in MPG, the calculator first converts your journey distance into UK (imperial) gallons used, by dividing miles by MPG. It then converts that into litres by multiplying by 4.54609 — the number of litres in one UK gallon (notably different from a US gallon, which is smaller, so always double check which one your car's figures use). Multiplying litres used by your price per litre gives the total cost, and dividing that by your distance gives cost per mile or per kilometre.

If you prefer to work in litres per 100km — common on newer cars and imported vehicles — the calculator uses that figure directly: litres used equals distance in kilometres divided by 100, multiplied by your L/100km figure.

Worked example

Say you're planning a 200-mile round trip in a car that does 45 MPG, with fuel priced at £1.45 per litre. You'd use 200 ÷ 45 = 4.44 UK gallons, which converts to around 20.2 litres. At £1.45 a litre, that's a total fuel cost of roughly £29.30 for the trip — about 14.6p per mile.

Now compare a less efficient car doing 32 MPG over the same distance: it would use around 28.4 litres, costing roughly £41.20 — over £11 more for exactly the same journey, purely down to the difference in fuel efficiency.

Why real-world MPG often differs from the official figure

The MPG figure quoted on a car's spec sheet — usually the WLTP combined figure on modern cars — is measured under standardised laboratory test conditions designed for fair comparison between models, not to predict your exact real-world consumption. Cold starts, town driving, hills, heavy loads, air conditioning and driving style can all reduce real-world MPG noticeably below the official number. For the most accurate cost estimate, use the average MPG shown on your car's own trip computer over a full tank or two, rather than the official spec figure.

Comparing petrol, diesel and hybrid running costs

Diesel cars typically return higher MPG than equivalent petrol cars, especially on motorway journeys, but diesel is often priced a few pence higher per litre — so the actual cost saving depends on both the MPG difference and the current price gap at the pump. Hybrids generally do best in stop-start town driving, where the electric motor can take over more often, and worst on sustained motorway runs where the engine does most of the work. Running this calculator with each car's real MPG and your typical fuel price is the simplest way to make a fair comparison for your own driving pattern.

Related calculators

Fuel is only part of the cost of owning a car — check our road tax calculator to see your annual VED bill, and factor both into your total motoring budget alongside insurance, servicing and depreciation.