Fuel Cost Calculator
Enter the trip distance, your fuel economy, and the pump price. Get the total cost, fuel used in litres and gallons, and cost per mile or km.
Total fuel cost
£11.67
- Fuel used (litres)
- 12.62
- Fuel used (US gallons)
- 3.33
- Fuel used (Imperial gallons)
- 2.78
- Cost per mile
- £0.12
- Cost per km
- £0.07
Distance is converted to km, fuel economy to litres-per-km, and price to per-litre using exact NIST factors (1 mi = 1.609344 km, 1 US gal = 3.785411784 L, 1 Imp gal = 4.54609 L). Fuel used = distance × consumption; cost = fuel used × price per litre.
How to use this calculator
Enter the trip distance and pick miles or kilometres. Enter your car’s fuel economy in whichever unit you have to hand — US mpg, UK (Imperial) mpg, litres per 100 km, or km per litre — and pick the matching unit. Finally, enter the pump price and the unit it is sold in (per US gallon, per Imperial gallon, or per litre). The calculator does all conversions internally, so you can mix units freely (UK miles + UK mpg + price per litre is a common combo).
How the calculation works
Everything is converted to a canonical pair — kilometres for distance and litres for fuel — using exact NIST factors: 1 mile = 1.609344 km, 1 US gallon = 3.785411784 L, 1 Imperial gallon = 4.54609 L. Fuel used (litres) = distance (km) × consumption (L/km). Cost = fuel used × price per litre. The breakdown shows the same fuel volume in litres, US gallons and Imperial gallons, plus the cost per mile and per km — useful for comparing across cars or planning a longer route.
Worked example
A 300-mile trip in a car that does 32 mpg-US, with petrol at $3.50 per US gallon: gallons used = 300 ÷ 32 = 9.375 US gal, so cost = 9.375 × $3.50 = $32.81. The same trip in a UK-spec car at 38 mpg-UK with petrol at £1.50 per litre: imperial gallons = 300 ÷ 38 ≈ 7.895, litres ≈ 7.895 × 4.54609 ≈ 35.89 L, cost ≈ £53.83. A 500 km drive at 7 L/100km with diesel at €1.65 per litre: 500 × 0.07 = 35 L, cost = 35 × €1.65 = €57.75.
Frequently asked questions
What is the difference between US mpg and UK mpg?
They use different gallons. A US gallon is 3.785411784 litres, while an Imperial (UK) gallon is 4.54609 litres — about 20% larger. So a car rated 30 mpg-US is roughly 36 mpg-UK for the same fuel economy. Always match the mpg unit to the country the figure was quoted in: US window stickers use mpg-US, UK manufacturer brochures use mpg-UK.
How do I convert L/100km to mpg?
They are reciprocal — lower L/100km means better economy, higher mpg means better economy. The exact conversions: mpg-US = 235.215 ÷ (L/100km), and mpg-UK = 282.481 ÷ (L/100km). So 8 L/100km is about 29.4 mpg-US or 35.3 mpg-UK. Just enter whichever unit your car displays — the calculator handles the maths.
Why does it ask for the price unit separately?
In the UK and most of Europe, fuel is sold by the litre even though cars are still rated in mpg. In the US it is sold by the US gallon. In Canada, fuel is sold by the litre but cars are sometimes rated in mpg-US. Letting you set the price unit independently of the economy unit means you can enter what you actually see on the pump and on the dashboard, with no manual conversion.
Does this account for traffic, hills or highway vs city driving?
No — it uses whatever fuel economy figure you provide as a flat rate over the whole trip. Real-world economy varies with speed, load, traffic and terrain. For a more realistic estimate on a mixed trip, use the lower of your car’s city and highway figures, or check your trip computer’s long-term average and use that.
Can I use this for a hybrid or plug-in hybrid?
For a regular hybrid, yes — use the manufacturer’s combined mpg or L/100km. For a plug-in hybrid running mostly on electricity, the petrol figure underestimates true running cost because the electric miles are not free either. For a pure EV this calculator is not the right tool — you would need kWh/mi or kWh/100km and an electricity price.
What is a typical fuel economy figure?
For petrol cars, 25–35 mpg-US (30–42 mpg-UK, or 7–9 L/100km) is typical for a mid-size saloon. Small economical cars can reach 40 mpg-US (48 mpg-UK, 6 L/100km). Large SUVs or pickups often manage just 18–22 mpg-US (22–26 mpg-UK, 11–13 L/100km). Use your car’s trip computer or recent fill-ups to get an accurate personal figure.