Method
How trip fuel cost is calculated
A trip fuel estimate needs three things: the distance, the vehicle’s fuel consumption, and the price of fuel. The arithmetic is simple, but the units are where most errors happen. UK fuel is priced per litre while economy may be quoted in imperial MPG; US fuel is priced per US gallon; European consumption is usually litres per 100 km.
The three formulas
United Kingdom
litres used = miles ÷ MPG (UK) × 4.54609
cost = litres used × (pence per litre ÷ 100)
Example: 100 miles ÷ 50 MPG UK × 4.54609
= 9.092 litres
9.092 × £1.45 = £13.18United States
US gallons used = miles ÷ MPG (US)
cost = US gallons used × dollars per US gallon
Example: 300 miles ÷ 30 MPG US = 10 US gallons
10 × $3.50 = $35.00Europe
litres used = km × (L/100 km) ÷ 100
cost = litres used × euros per litre
Example: 500 km × 6.5 ÷ 100 = 32.5 litres
32.5 × €1.75 = €56.88Do not multiply price by MPG
Worked comparison
| Market | Inputs | Fuel used | Total | Per mile / km |
|---|---|---|---|---|
| UK | 100 mi · 50 MPG UK · 145 p/l | 9.09 L | £13.18 | £0.132/mi |
| US | 300 mi · 30 MPG US · $3.50/gal | 10 US gal | US$35.00 | US$0.117/mi |
| Europe | 500 km · 6.5 L/100 km · €1.75/l | 32.5 L | €56.88 | €0.114/km |
Cost per mile and cost per 100 km
Total cost is useful for a specific trip. Cost per mile or per 100 km is useful for comparing journeys of different lengths. The conversion between them is:
cost per 100 km = cost per mile × 62.137119 cost per 100 km = cost per km × 100 cost per mile = cost per km × 1.609344
The calculator shows both because UK and US results are naturally per mile, while European results are naturally per kilometre or per 100 km.
Round trips and one-way trips
A round trip doubles the distance. If you enter the one-way distance, the calculator must double it before applying consumption; if you enter the total distance, it must not. The calculator makes this explicit with a round-trip checkbox rather than guessing.
What the estimate excludes
- Tolls, vignettes, ferries, congestion charges and parking.
- Servicing, repairs, tyres, insurance, depreciation and finance.
- Cold starts, traffic, hills, roof boxes, heavy loads and air conditioning.
- Price differences between fuel grades or between stations on the route.
Published consumption is a test-cycle figure. Real consumption can be higher or lower. The result is an estimate, not a quote.
Run the numbers
The calculator uses the formulas above and switches units with the market selection.
Open the fuel cost calculatorSources
- GOV.UK — weekly road fuel prices — UK price statistics for context, not a live station price.
- US EIA — gasoline and diesel prices — US regional and national averages.
- European Commission — Weekly Oil Bulletin — EU fuel price monitoring.
Page last reviewed: . Formulas are covered by automated tests. Prices are inputs, not live data.