UK Fuel Cost Calculator
Calculate your trip cost or annual fuel spend — petrol, diesel, or electric.
How does the fuel cost calculator work?
The trip calculator works out the cost of a single journey from your distance, fuel economy and fuel price. The annual calculator does the same for a year of driving at your mileage, and also compares petrol, diesel and electric using reference efficiencies, so you can see how the three fuel types compare.
For petrol and diesel, the calculator converts your MPG into litres used (1 UK gallon = 4.546 litres) and multiplies by the price per litre. For electric cars it works from miles per kWh and your electricity price per kWh. When you switch the fuel type, the labels and default prices update to match.
The defaults are UK averages on 14 October 2026: petrol 174p and diesel 199p a litre (Fuel Finder UK), and 26p/kWh for electricity (the Ofgem price-cap average from 1 October 2026 is 26.32p/kWh). Your own prices will differ.
3 worked examples
Example 1 — Weekend trip, petrol car
A 150-mile journey in a petrol car averaging 35 MPG, at 174p a litre.
(150 ÷ 35) × 4.546 = 19.5 litres
Cost:19.48 × £1.74 = £33.90 for the trip (≈22.6p per mile)
Example 2 — Annual diesel commuter
A diesel estate covering 12,000 miles a year at 48 MPG, with diesel at 199p a litre.
(12,000 ÷ 48) × 4.546 = 1,137 litres a year
Cost:1,136.5 × £1.99 = £2,262 a year (≈£188 a month, 18.8p per mile)
Example 3 — Annual EV, home charging
An electric car doing 8,000 miles a year at 3.5 mi/kWh, with home electricity at 26p/kWh.
8,000 ÷ 3.5 = 2,286 kWh a year
Cost:2,285.7 × £0.26 = £594 a year (≈£50 a month, 7.4p per mile)
Petrol vs diesel vs electric: cost per mile
At the default prices, a home-charged electric car costs about 7p a mile, against roughly 20–23p for a typical petrol or diesel car. Public charging costs more per kWh than home charging and varies a lot between networks, so the gap shrinks if you charge away from home. Check the tariff of the network you use.
| Fuel type | Efficiency | Cost per mile |
|---|---|---|
| Petrol | 35 MPG | 22.6p |
| Petrol (efficient) | 50 MPG | 15.8p |
| Diesel | 45 MPG | 20.1p |
| Diesel (efficient) | 60 MPG | 15.1p |
| Electric, home charging | 3.5 mi/kWh | 7.4p |
For a fuller comparison, see Fuel Cost Per Mile UK and the EV vs Petrol Calculator.
How to measure your real-world MPG
Fill your tank to the brim, reset your trip counter, and drive normally. At the next fill-up, brim the tank again and note the litres added. Divide the miles driven by the litres and multiply by 4.546 to get UK MPG. A car's dashboard average is a handy shortcut once you've checked it against a brim-to-brim test.
Official MPG figures are often optimistic. They come from standardised tests, and real driving, especially in town or at motorway speeds, often gives a lower figure. Use your own brim-to-brim result, or an owner-reported figure, for a realistic estimate.
Common calculation mistakes
Using the manufacturer's MPG instead of real-world MPG
Official figures are often more optimistic than real driving. Use a figure you've measured, or one from owners of the same car.
Using the wrong price for the fuel type
Diesel currently costs more per litre than petrol. Pairing a diesel car's MPG with the petrol price understates its cost, so always match the price to the fuel.
Not adjusting an EV estimate for where you charge
The default electricity price is a home-charging figure. If you charge on public networks, enter the price you actually pay, or the result will be too low. The EV vs Petrol Calculator can compare the two.
Guessing your annual mileage
Drivers often underestimate their mileage, especially if it includes occasional long trips. Check the mileage recorded at your last two MOTs for your real yearly figure.
Tips to reduce your fuel costs
- Keep tyres at the recommended pressure. Under-inflated tyres increase rolling resistance and fuel use.
- Remove roof boxes and racks when you're not using them to cut drag.
- Accelerate and brake smoothly. Harsh driving uses more fuel.
- Use cruise control on motorways to hold a steady speed.
- Compare nearby forecourts using a price-comparison app or website. Motorway services are often more expensive than other forecourts.
- Charge an electric car at home where you can, as public charging usually costs more per kWh.
How we calculate
Petrol/diesel cost = (distance or mileage ÷ MPG) × 4.546 × fuel price per litre
Electric cost = (distance or mileage ÷ mi/kWh) × electricity price per kWh
The trip calculator applies this once for your distance. The annual calculator applies it to your yearly mileage. The comparison bars apply the same formula three times with fixed reference efficiencies (35 MPG petrol, 45 MPG diesel, 3.5 mi/kWh electric) and the default prices (petrol 174p, diesel 199p, electricity 26p/kWh), so you can see how the three fuel types compare.
Frequently asked questions
What is the average petrol price in the UK?
On 14 October 2026 the UK average was about 174.1p a litre for petrol and 199.1p for diesel, according to Fuel Finder UK. Prices vary by region and retailer and change quickly, so check a live tracker for today's figure.
How do I calculate my car's real-world MPG?
Fill the tank to the brim, reset your trip counter, drive normally, then brim the tank again. Divide the miles driven by the litres added, then multiply by 4.546 to get UK MPG.
Is electric cheaper per mile than petrol or diesel?
With home charging at the default prices, yes: about 7p a mile against 20–23p for a typical petrol or diesel car. Public charging usually costs more per kWh, so the gap depends on where you charge.
Why does my actual fuel cost differ from the calculator?
The usual reasons are using an official MPG figure instead of a real-world one, an out-of-date fuel price, or a different mix of town and motorway driving. Enter your own measured MPG and the price you actually pay.
Does the annual calculator account for seasonal price changes?
No. It uses a single price for the whole year, so treat the result as an estimate at today's price, not a forecast.
References & data sources
- Fuel Finder UK — UK Fuel Price Index. Average petrol (174.1p) and diesel (199.1p) prices on 14 October 2026, from the government Fuel Finder feed.
- Ofgem — Energy price cap, 1 October to 31 December 2026. Average electricity unit rate of 26.32p/kWh, used to set the 26p default.
- RAC Fuel Watch. A live tracker for current fuel prices, suggested for checking today's figure.
Prices were checked on 15 October 2026 and change often. Use the price you actually pay for the most accurate result.
Prakash
Prakash is the founder and editor of UK Driving Tools. He maintains the site's calculators and guides and checks the rates and rules they use against official UK sources, such as GOV.UK, the DVLA, HMRC and Transport for London, before publishing.
Pages are drafted with the help of AI tools and then checked by the editor. He isn't a lawyer, accountant or UK-qualified adviser, so every page lists its sources and states what its calculator can't tell you. Nothing on this site is legal or financial advice.
Pages on UK Driving Tools are drafted with the help of AI tools. Before publishing, the figures and rules on each page are checked against the official source named on the page, and calculator examples are tested against the working formula. Pages are updated when rates or rules change. Our Editorial Policy explains the full process, including how to report a mistake.
Spotted a mistake or an out-of-date rate? Let us know and we'll check it against the official source.