Fuel Cost Calculator

Quick answer

Fuel cost per mile = price per litre × 4.546 ÷ your car's mpg. A 50 mpg car at £1.50 a litre costs about 13.6p a mile, so a 200-mile round trip costs roughly £27.28. Enter your own trip above.

Price any journey before you set off

Enter your distance, your car's miles per gallon and the current pump price into the fuel cost calculator above, and it returns the cost of the trip. Change any one of the three inputs and the result updates, so you can test a cheaper route, a more economical driving style, or a fill-up at a supermarket forecourt versus a motorway services.

How the fuel cost calculation works

The maths behind a petrol cost calculator is short, but the unit juggling trips people up. Your MPG is measured in miles per imperial gallon, yet you buy fuel in litres. One imperial gallon is 4.54609 litres, so every calculation has to convert between the two.

The formula, in plain words, is:

• Gallons used = distance in miles ÷ MPG
• Litres used = gallons used × 4.546
• Journey cost = litres used × price per litre

You can fold that into a single line: cost = (miles ÷ MPG) × 4.546 × price-per-litre-in-pounds. If you prefer to think per mile, divide the journey cost by the miles and you get your pence-per-mile fuel figure, which is handy for budgeting and for comparing cars.

A quick note on MPG itself. The official figure on a car's spec sheet comes from a standardised lab test (WLTP) and is usually optimistic compared with real-world driving. Town traffic, a roof box, a full boot, cold weather and a heavy right foot all push your real MPG down. For an honest estimate, work out your own MPG: note the miles between two fill-ups, then divide by the gallons you put in (litres ÷ 4.546). Use that number here rather than the brochure figure.

Diesel and petrol use exactly the same formula; only the MPG and the pump price differ. Diesels typically return more miles per gallon but diesel often costs a few pence per litre more, so the cheaper-to-run answer depends on both figures together, not just the MPG.

Worked example: a five-day commute

Picture Sarah, a nurse in Leeds who drives 24 miles to the hospital and 24 miles home, five days a week. Her petrol hatchback returns a real-world 45 MPG and her local forecourt is charging 140p a litre.

• Weekly distance: 48 miles × 5 = 240 miles
• Gallons used: 240 ÷ 45 = 5.33 gallons
• Litres used: 5.33 × 4.546 = 24.25 litres
• Weekly cost: 24.25 × £1.40 = £33.94

Over a 46-week working year that is roughly £1,561 in fuel just getting to work. Knowing the number makes decisions concrete: a colleague to car-share with, or a switch to a 55 MPG car, would cut that weekly bill to about £27.78 and save her over £280 a year on the same commute.

Worked example: a long motorway trip

Now take Daniel, driving 300 miles from Bristol to Newcastle in a diesel estate that does 52 MPG on a steady motorway run, with diesel at 148p a litre.

• Gallons used: 300 ÷ 52 = 5.77 gallons
• Litres used: 5.77 × 4.546 = 26.23 litres
• One-way cost: 26.23 × £1.48 = £38.82

The return leg costs the same, so the round trip is about £77.64 in fuel. Split between four people sharing the car, that is roughly £19.41 each, far less than the train for most groups. This is where a journey cost calculator earns its keep: it turns a vague "it'll cost a bit" into a figure you can split fairly or claim back.

Claiming fuel back: business mileage and EVs

If some of those miles are for work, you may be able to claim them. Employees using their own car for business journeys can claim a tax-free mileage allowance from their employer, or tax relief from HMRC if the employer pays less than the approved rate. That allowance is a flat pence-per-mile figure meant to cover fuel and wear, so it is not the same as your raw fuel cost here. Work out what you are owed with our mileage allowance calculator, and keep a running log with the mileage tracker so your claim stands up if HMRC asks. The official rules are on the gov.uk business mileage pages.

Thinking of going electric? Charging is priced per kWh, not per litre, so the comparison needs a different sum. Our EV charging cost calculator works out the cost of a journey on electricity, which lets you put the two fuels side by side honestly. To see the full running cost of any car including tax and depreciation, the cost per mile calculator goes a step further than fuel alone.

Practical ways to cut the figure down

Small changes move the number more than people expect, because fuel cost scales directly with both consumption and price:

• Drive for economy. Easing off above 60mph, smooth acceleration and correct tyre pressures can lift real MPG by 10 to 20 per cent, which feeds straight through to a lower trip cost.
• Shop around for fuel. Supermarket forecourts are often several pence a litre cheaper than motorway services. On a 50-litre fill, 6p a litre is £3 saved each time.
• Lose dead weight and drag. Roof boxes and bars hurt motorway economy noticeably; take them off when not in use.
• Combine trips. A cold engine uses far more fuel in the first couple of miles, so one longer chained trip beats several short cold starts.

Once you know your weekly fuel spend, fold it into a wider plan. The budget calculator helps you sit fuel alongside the rest of your outgoings rather than treating it as an afterthought.

Common mistakes to avoid

A few errors quietly throw the result off:

• Mixing up gallons. A US gallon is 3.785 litres, not 4.546. UK MPG uses the imperial gallon, so always convert with 4.546 or your cost lands about 17 per cent too low.
• Using the brochure MPG. Lab figures flatter most cars. Measure your own MPG over a few tanks for a realistic answer.
• Pricing in pence but reading in pounds. 140p per litre is £1.40, not £140. Keep the decimal point straight.
• Forgetting the return leg. Enter the full round-trip distance, or remember to double a one-way result.
• Assuming diesel is always cheaper to run. Higher MPG can be cancelled out by a higher pump price and a pricier service bill, so compare the total, not the headline MPG.

These estimates are for guidance only and are not personal tax or financial advice. Fuel prices change daily, so re-check the pump price for an accurate result.

Related calculators worth a look

To go further than fuel alone, try the cost per mile calculator for total running costs, the EV charging cost calculator to compare electric driving, and the mileage allowance calculator if any of your driving is for work and could be claimed back.

Pence per mile, by efficiency and fuel price

Business drivers: log trips with the mileage tracker and check GOV.UK mileage rates. Electric? Compare with the EV charging calculator.