Work out the fuel cost of a journey from the miles, your car’s mpg and the price per litre. A 200-mile trip there and back (400 miles) in a car that does 45 mpg needs about 40.4 litres; at the UK average petrol price of 174.7p that is £70.60.
Fuel Cost Calculator
Default prices: UK averages on 12 October 2026 (government Fuel Finder data)
- Total distance
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- Fuel needed
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- Cost per mile
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- Cost per person
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Converting mpg to litres
UK mpg uses the imperial gallon, which is 4.54609 litres (a US gallon is only 3.785 litres). The calculator works out fuel used as miles ÷ mpg × 4.54609, then multiplies by the pump price.
- Litres = miles ÷ mpg × 4.54609
- Cost = litres × price per litre
- Cost per mile = price per litre × 4.54609 ÷ mpg
Cost per 100 miles
| Fuel economy | Petrol at 174.7p | Diesel at 199.8p |
|---|---|---|
| 30 mpg | £26.47 | £30.28 |
| 40 mpg | £19.86 | £22.71 |
| 50 mpg | £15.88 | £18.17 |
| 60 mpg | £13.24 | £15.14 |
A diesel that does 60 mpg costs about 74p less per 100 miles than a petrol car doing 50 mpg, even with diesel at 199.8p a litre.
Where the prices come from
Default prices are the UK averages for petrol (E10) and diesel (B7) on 12 October 2026, calculated from the government’s Fuel Finder station price feed. Prices change daily and vary by area, so enter what you pay.
FAQs
Can I claim mileage for business journeys?
If you use your own car for work, HMRC’s approved mileage allowance is 45p a mile for the first 10,000 business miles in a tax year and 25p after that. Compare it with your real cost per mile from the calculator.
How do I find my real mpg?
Fill the tank, reset the trip meter, drive normally, then refill. Divide the miles driven by the litres added and multiply by 4.54609 to get mpg.
Related calculators
Sources
- Fuel Finder UK: UK fuel price index (government Fuel Finder feed) · 12 October 2026
- GOV.UK: Approved mileage allowance payments
Figures current as of 12 October 2026
Each formula is checked against a separate test sheet with at least three worked examples. Results are estimates based on the numbers you enter and the published rules; your actual figures may differ. This is general information, not financial or tax advice.
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