Fuel Cost Calculator
Work out the fuel cost of a trip or your commute in miles or km, and compare a petrol or diesel car with an electric car per trip, month and year.
Reviewed by Dany, RightSums team · Updated
Runs in your browser. Free, no sign-up.
car-travel · Daily life · UK & US
Pick one trip or a regular commute, then enter the distance in miles or kilometres. Add your fuel economy in UK mpg, US mpg or litres per 100 km, and the fuel price per litre or per gallon. Prices start at the latest official averages: DESNZ weekly pump prices in the UK and EIA weekly prices in the US, with the date shown. Tick the electric car box to add its efficiency, how much you charge at home and the public price you pay. The home rate starts at the Ofgem price cap or the EIA residential average. You see both cars side by side per trip or day, per month and per year, plus the cost per mile. It covers energy, parking and tolls only, not servicing, insurance or depreciation.
Accepted inputs
- Mode: one trip or regular commute
- Distance in miles or kilometres, one way or return
- Days a week, weeks a year and parking or tolls a day (commute)
- People sharing and trips a month (one trip)
- Fuel economy in UK mpg, US mpg or L/100km
- Fuel price per litre, per US gallon or per UK gallon, in £ or $
- Electric car efficiency in miles/kWh, kWh/100 miles or kWh/100 km
- Home and public charging share and price per kWh
- Charging loss assumption
Outputs
- Petrol or diesel cost per trip or day, week, month and year
- Electric car cost for the same distance
- Difference per trip, month and year
- Cost per mile or km for both cars
- Fuel used in litres, UK gallons and US gallons, and kWh
- Cost per person for shared trips
How to use the Fuel Cost Calculator
- Choose one trip or a regular commute, then enter the distance in miles or kilometres and, for a commute, your days a week, weeks a year and any parking or tolls.
- Enter your fuel economy in UK mpg, US mpg or litres per 100 km, and check the fuel price, which starts at the latest DESNZ or EIA average with its date.
- Tick the electric car box and enter its efficiency, the share you charge at home, your home and public prices per kWh and any charging loss you want to allow for.
- Read both cars side by side per trip or day, per month and per year, with the cost per mile and the difference between them.
Frequently asked questions
How much does it cost to charge an electric car vs petrol per mile?
About 7.5p a mile charged at home, against about 17.4p for petrol. An electric car doing 3.5 miles per kWh at the Ofgem cap of 26.32p from 1 October 2026 costs £7.52 per 100 miles. A 45 mpg petrol car at 172.01p a litre (DESNZ, week of 21 September 2026) costs £17.38. Charging 20% at a 70p public charger raises the electric cost to 10.0p a mile.
How much does my commute cost in fuel a year?
A 20-mile round trip, 5 days a week for 46 weeks, at 45 mpg and 172.01p a litre (DESNZ, week of 21 September 2026) costs £799 a year in petrol, or £66.61 a month. Add £5 a day parking and it becomes £1,949 a year. The same commute in an electric car charged at home costs £346 a year before parking.
Why does the commute use 46 weeks a year?
UK workers are entitled to 5.6 weeks' paid holiday a year, so 52 weeks less 5.6 leaves 46.4 working weeks, which the calculator rounds to 46. The number is shown and you can change it. Lower it for extra holiday or weeks you work from home. In the US, enter the weeks you actually drive in.
How much gas does a 300-mile road trip cost?
At 30 US mpg you use 10 US gallons, which costs $44.78 at the EIA average of $4.478 a gallon for the week of 21 September 2026. Split three ways that is $14.93 each. An electric car using 30 kWh per 100 miles at 18.31 cents a kWh would cost $16.48 for the same drive.
What is the difference between UK mpg, US mpg and L/100km?
A UK gallon is 4.54609 litres and a US gallon is 3.785411784 litres, so 45 UK mpg equals 37.5 US mpg or 6.28 litres per 100 km. Pick the wrong one and the cost is out by about a sixth: 100 miles at 45 mpg costs £17.38 as UK mpg but £14.47 as US mpg.
Sources
The rates and rules in this tool come from:
- legislation.gov.uk: Weights and Measures Act 1985
- NIST: NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity or…
- GOV.UK: Holiday entitlement: Entitlement
- US EPA: Fuel Economy and EV Range Testing
- fueleconomy.gov: All-Electric Vehicles
- GOV.UK: Weekly road fuel prices
- US Energy Information Administration: Gasoline and Diesel Fuel Update
- Ofgem: Energy price cap unit rates and standing charges
- US Energy Information Administration: Electric Power Monthly
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