What will my petrol cost for a journey or a year, at my real mpg?
Fuel cost for a journey or a year, and your real mpg. Free, no sign-up, nothing leaves your browser.
Journey cost
Type the miles to get there. Pick Return and we double them, so the drive home counts. A route planner gives you the miles; we don't look them up.
Everyone chipping in, driver included. We split the total you see, then tell you if the rounded shares miss it, and by how much.
Yearly cost
What you usually drive, per week, month or year. For term-time school runs, type the year's miles. A year here is 52 weeks or 12 months.
Your mpg
Reset the trip meter when you fill the tank right up, then read it at the next full fill-up.
Note the odometer (the mileometer) when you fill right up. At a later full fill-up, note it again. Tenths of a mile count.
Leave out the first fill: it only sets the starting line. Add every litre after it, top-ups included, up to the last full tank. Several fill-ups give a steadier figure than one.
Every receipt after the first fill, top-ups too, up to the last full tank.
10 receipts is the limit.
Fuel for this journey
A year here is 52 weeks or 12 months, and the month and week come from the rounded year.
One tank is a small sample. The pump clicks off at a slightly different point each time, so a few fill-ups in a row give a steadier figure.
That's outside 5 to 100 mpg, our usual-range check. Check the miles and the receipts: the first fill's litres don't belong here.
Has your mpg dropped and stayed down? A garage can look at why. Browse Auto Repair Shops or Car Tune-Up near you.
Example: 200 miles each way, return, at 42.8 mpg and 158.9p a litre comes to £67.52.
£67.52
400 miles return (200 each way) at 42.8 mpg and 158.9p a litre
42.49 litres
16.9p a mile
At 42.8 mpg your car uses 6.6 litres every 100 km.
Miles x 4.54609 / mpg = litres. Litres x price in pence / 100 = cost in pounds.
Miles a year x 4.54609 / mpg x price in pence / 100 = cost a year in pounds. A month is the year / 12, a week the year / 52.
Miles x 4.54609 / litres pumped = mpg.
How the fuel cost calculator works
You're about to set off somewhere and you want one number for the fuel.
The UK makes that harder than it looks. The pump sells litres, the sign shows pence, and your car's economy comes in miles per gallon, a unit the pump doesn't use. The calculator does that conversion with the exact gallon and rounds to the penny once, at the end.
Miles. Type the miles to get there. Pick Return and they count twice, because the drive home burns fuel too.
Your mpg. Your car's own figure, in UK gallons. The Your mpg tab works it out from two full tanks and the receipts in between, and one tap carries it across.
The pump price, in pence. Type it as the sign shows it: 158.9, not £1.589. We never fill in a price. Pump prices move week to week, so use the price you'll pay.
Litres. Miles divided by mpg gives gallons, and each gallon is 4.54609 litres. The calculator shows them to two decimal places, and the cost comes from that figure.
Cost, rounded once. Litres times the price in pence, divided by 100 for pounds, then rounded to the penny at the end. That's why 200 miles each way at 42.8 mpg and 158.9p comes to £67.52 for the return. Round the one-way £33.75 first and double it, and you'd say £67.50.
The split. The rounded total, divided by everyone in the car. Three people pay £22.51 each. That comes to £67.53, and the calculator tells you the shares are a penny over.
Yearly cost is the same sum, bigger. Type what you drive in a week, a month or a year. A year counts as 52 weeks or 12 months, and the month and the week come from the rounded year. An 80-mile week of school runs at 38.0 mpg and 161.9p comes to £805.74 a year and £67.15 a month. If the school run stops for the holidays, type the year's miles.
It's arithmetic on your numbers, not a forecast, and it's fuel only. Parking, tolls and any clean air zone charge come on top. Our clean air zone checker tells you whether your car pays in a zone.
Litres at the pump, mpg in the advert
UK law still defines the gallon: exactly 4.54609 litres, in the Weights and Measures Act 1985. It sits in a list of units that "may not be used for trade except as supplementary indications". So the pump sells you litres, and the advert still talks mpg.
Printed new-car brochures have to give the official fuel consumption in mpg and in litres per 100 km or kilometres per litre, to one decimal place. That's why every mpg the calculator shows comes with litres per 100 km beside it.
Americans use a different gallon. Theirs is about a sixth smaller, so the same car gets a lower mpg figure in the US. Use a US calculator with a UK mpg and it budgets too little fuel.
How to work out mpg from your fill-ups
The advert's mpg comes from a test. Yours comes from the forecourt, and it takes two full tanks. The method is simple. The bit people get wrong is the top-up in the middle.
Fill the tank until the pump clicks off. Note the odometer, or reset the trip meter.
Drive the way you normally do. If you top up along the way, keep the receipt.
Fill until it clicks off again. Note the odometer and the litres.
Add every litre pumped after the first fill: the top-ups and the last fill. Leave out the first fill, because it only filled the tank to the starting line. Miles times 4.54609, divided by those litres, is your mpg.
Miss a top-up and the figure flatters the car. 484.6 miles on 15.42 plus 32.87 litres is 45.6 mpg. Forget the 15.42 and the same car seems to do 67.0.
For a steadier number, measure over several fill-ups: add all the miles, add all the litres, divide once. Don't average each tank's mpg. A tank at 45.5 mpg and the next at 30.3 average 37.9, but the car went 572 miles on 65.2 litres, which is 39.9. Plan a 572-mile drive at 37.9 and you'd budget 68.6 litres for the 65.2 it really takes.
A plug-in hybrid's fill-up mpg counts only the fuel. Whatever it charged from the wall isn't on the receipts.
The odometer has to be right, too. On tyres that aren't the original size it can read off, and your mpg is out by the same proportion.
Who this is for
Anyone splitting petrol money on a lift share or a weekend away. Parents adding up a year of school runs, and commuters weighing a new job further out. And anyone sitting on a stack of fuel receipts who wants to know what the car really does to the gallon.
Driver questions about fuel cost and mpg
How do I work out the fuel cost of a journey?
Divide the miles by your mpg, multiply by 4.54609 to turn gallons into litres, then multiply by the pump price in pence and divide by 100 for pounds. A 400-mile return at 42.8 mpg takes about 42.49 litres, and at 158.9p a litre that's £67.52. Count the drive home, use the mpg your car really does, and round once at the end, not leg by leg.
How do you work out mpg in the UK?
Fill right up and note the miles. Drive, fill right up again and note the litres. Divide the litres by 4.54609 to get UK gallons, then divide the miles by that. Topped up in between? Add those litres too. The Your mpg tab does the sum and shows litres per 100 km beside it.
Why is UK mpg different from US mpg?
The gallons aren't the same size. A UK gallon is 4.54609 litres and a US gallon 3.785411784, about a sixth smaller. So the same car shows a lower figure in US mpg: 400 miles on 40 litres is 45.5 mpg here and 37.9 in America. Feed a UK mpg into an American calculator and it budgets about 17% too little fuel.
How many litres are in a UK gallon?
4.54609, exactly. That's the definition in the Weights and Measures Act 1985. A US gallon holds 3.785411784 litres, which is why American mpg figures look worse for the same car. Pumps here sell by the litre, so the calculator turns your mpg into litres with that 4.54609.
How do I convert mpg to litres per 100 km?
Divide 282.48 by your UK mpg. 42.8 mpg is 6.6 litres per 100 km, and the same sum runs the other way. You'll see both figures because printed new-car brochures have to give fuel consumption in mpg and in litres per 100 km or kilometres per litre. The calculator shows litres per 100 km beside every mpg, so you never have to convert.
How much does petrol cost per mile?
The pump price times 4.54609, divided by your mpg. At 158.9p a litre and 42.8 mpg, each mile burns about 16.9p of fuel, so 100 miles is about £16.90. That's fuel alone: no tyres, servicing or wear. Diesel works the same way with the diesel price.
How much petrol money should I give someone?
Start from the fuel for the whole journey, the drive back included, and split it between everyone in the car, driver too. Set People sharing the fuel cost and the calculator divides the rounded total, then rounds each share. Three people on a £67.52 return pay £22.51 each. That's £67.53, and we tell you the shares are a penny over, so nobody argues about where it went.
Why is my mpg lower than advertised?
Because the advert's figure isn't yours. It's an official figure from a standard test, which helps you compare cars and gives you a rough starting point for budgeting. Your own driving isn't that test. The real figure for your car takes two full tanks and the receipts in between.
Is fuel cost per mile the same as HMRC's mileage rate?
No. HMRC has two per-mile schemes, and neither is what your car burns. Mileage Allowance Payments are what an employer pays for business journeys in your own vehicle. Advisory fuel rates apply only to company cars, and HMRC reviews them every quarter. We don't print either rate here. GOV.UK has the current figures.
Does anything I type get saved or sent?
No. The sums run in your browser, on your device. Nothing you type is sent anywhere or stored, and the next visit starts blank. To keep a result, copy it or print it.
Petrol and diesel cost per mile, per month and per year
A journey, a month of commuting and a year of driving are the same sum at three sizes. Fuel cost per mile is the pump price times 4.54609, divided by your mpg. At 161.9p and 38.0 mpg, that's 19.4p a mile. Multiply your year's litres by the price in pence and divide by 100 for pounds. A month is the year divided by 12 and a week the year divided by 52, so typing your miles a week gets you all three.
Eyeing up a thirstier car? Keep the miles and the price, change only the mpg, and compare the two yearly totals. The gap is what the extra fuel costs you, before insurance or anything else. Road tax is a separate bill too, and our car tax calculator works that one out.
Sources and last checked
- Weights and Measures Act 1985, Schedule 1, on legislation.gov.uk: the gallon (4.54609 litres) and the mile.
- The Passenger Car (Fuel Consumption and CO2 Emissions Information) Regulations 2001, Schedule 4: mpg and litres per 100 km in new-car brochures.
- HMRC, Advisory fuel rates, on GOV.UK: company cars only, reviewed quarterly.
- HMRC, Travel - mileage and fuel rates and allowances, on GOV.UK: the approved mileage rates for your own vehicle.
- Department for Energy Security and Net Zero, Weekly road fuel prices: average pump prices each week, if you want a reference before you fill up. We link it and don't copy it.
- Units: miles and litres as you type them, the gallon at 4.54609 litres (unit profile fuel-unit-profiles, version 2026-10-07).
Last checked 8 October 2026.
More free tools for your car
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- Clean air zone checker: will I have to pay?
Zone charges are the other cost of a drive into some cities, and they depend on the car.
- Car tax calculator: what will my road tax be?
Road tax is the yearly bill that fuel doesn't cover.
Worth a bookmark if you share lifts or keep your fuel receipts.