Last reviewed 23 October 2026
How to use the fuel cost calculator
- Choose petrol, diesel or electric. We fill in typical example values, which you should replace with your own.
- Enter the distance. Use a route planner for the one-way distance, then tick "return journey" if you are coming back the same way.
- Enter your car's economy in mpg (UK or US), litres per 100 km, or for electric cars miles per kWh.
- Enter the price per litre, per gallon or per kWh, and how many people are sharing the cost.
The result updates as you type and shows the total cost, the cost per person, how much fuel or electricity you will use and the cost per mile or kilometre.
The formula, with a worked example
For a petrol or diesel car measured in UK mpg:
Fuel cost = (distance ÷ mpg) × 4.546 × price per litre
A 200-mile trip in a car that does 45 mpg, with petrol at £1.74 a litre:
- 200 ÷ 45 = 4.44 gallons
- 4.44 × 4.546 = 20.2 litres
- 20.2 litres × £1.74 ≈ £35.16
For an electric car: 200 miles ÷ 3.5 miles per kWh = 57.1 kWh. At 28p per kWh that is £16.00; at 79p per kWh on a rapid charger, it is about £45.
A UK gallon (4.546 litres) is about 20% bigger than a US gallon (3.785 litres), so the same car shows a higher mpg figure in the UK than in the US. Make sure you choose the right one.
Typical fuel economy figures
If you don't know your car's real-world economy, these rough ranges are a reasonable starting point. Your own figures will vary with driving style, speed, load and weather.
| Car type | Typical economy |
|---|---|
| Small petrol hatchback | 45–55 mpg (UK) |
| Family petrol car or small SUV | 38–48 mpg (UK) |
| Diesel estate or family car | 50–60 mpg (UK) |
| Large SUV or people carrier | 28–38 mpg (UK) |
| Hybrid | 50–65 mpg (UK) |
| Electric car | 3–4.5 miles per kWh |
Converting between mpg and litres per 100 km
| mpg (UK) | mpg (US) | L/100 km |
|---|---|---|
| 30 | 25.0 | 9.4 |
| 40 | 33.3 | 7.1 |
| 50 | 41.6 | 5.6 |
| 60 | 50.0 | 4.7 |
To convert yourself: L/100 km = 282.5 ÷ UK mpg, or 235.2 ÷ US mpg.
Ways to cut your fuel cost
- Fill up before the motorway. Motorway service stations typically charge well above the national average. Supermarket forecourts are usually among the cheapest.
- Slow down slightly. Cruising at 60–65 mph instead of 70–75 mph can noticeably improve economy on long journeys.
- Check your tyres. Under-inflated tyres increase fuel use. Inflate to the "full load" pressure in your handbook if the car is packed.
- Take off the roof box when you don't need it. It adds drag even when empty.
- EV drivers: charge at home or at destination chargers where possible, and use rapid chargers only to top up what you need.
Frequently asked questions
How do I work out the fuel cost of a journey?
Divide the distance by your car's miles per gallon to get gallons used, convert gallons to litres (1 UK gallon is 4.546 litres), then multiply by the price per litre. The calculator does this for you and handles return trips, kilometres and US gallons.
What mpg should I use?
Use the real-world figure from your car's trip computer or fuel records if you have it. Official figures are often optimistic. Motorway driving at 70 mph usually uses more fuel than steady 50–60 mph driving, and a fully loaded car or roof box will lower your mpg.
Is it cheaper to drive or fly?
For two or more people, driving is often cheaper on fuel alone, especially in an efficient car. Remember to add tolls, parking, ferries and overnight stops, and compare against the total cost of flights, including luggage and travel to and from the airport.
How do I split fuel costs fairly with passengers?
Enter the number of people sharing the cost and the calculator divides the total equally. Some drivers include a little extra for wear and tear; HMRC's approved mileage rates are a common reference point in the UK for business travel.
How much does it cost to charge an electric car for a trip?
Multiply the energy used (distance divided by miles per kWh) by your electricity price. Home charging, especially on an overnight EV tariff, is usually much cheaper than public rapid chargers, so try both prices in the calculator.
Example prices are UK averages for October 2026 and are for illustration only. Fuel prices change often and vary between stations, so enter the price you will actually pay.