Calculate the cost of your journey based on distance and fuel efficiency
Fuel costs are one of the largest ongoing expenses for UK motorists, with the average driver spending over GBP 1,500 per year on petrol or diesel. Understanding exactly how much a journey will cost helps you budget for road trips, compare routes, and make informed decisions about your driving habits. The UK uses imperial gallons for fuel efficiency (miles per gallon), but fuel is sold in litres at the pump. This means calculating your actual journey cost requires converting between the two systems. Our fuel cost calculator handles this conversion automatically, using the correct imperial gallon figure of 4.546 litres -- not the smaller US gallon of 3.785 litres that many online calculators incorrectly use. Whether you are planning a long motorway journey or simply want to know how much your daily commute costs, enter your distance, your car's MPG rating, and the current price at the pump to get an instant cost breakdown.
To calculate the fuel cost of your journey: 1. Enter the total distance of your journey in miles. You can find this using a route planner like Google Maps. For return journeys, remember to double the one-way distance. 2. Enter your vehicle's fuel efficiency in miles per gallon (MPG). You can find this in your car's handbook, on the manufacturer's website, or by checking the trip computer display in your vehicle. Real-world MPG is typically 10-20% lower than the official WLTP figure. 3. Enter the current fuel price in pence per litre. Check local forecourt prices or use an app like PetrolPrices to find the cheapest fuel near you. 4. Select your fuel type. While this does not affect the core calculation, it helps label your results correctly. 5. Review the results showing your total fuel cost, the number of litres you will use, and the cost per mile. Use the cost per mile figure to compare different routes or vehicles.
The fuel cost formula converts between imperial gallons and litres: Gallons used = distance (miles) / fuel efficiency (MPG) Litres used = gallons used x 4.546 (litres per imperial gallon) Total cost (pence) = litres used x fuel price (pence per litre) Total cost (GBP) = total cost (pence) / 100 Cost per mile = total cost / distance For example, a 100-mile journey in a car achieving 40 MPG with fuel at 145 pence per litre: gallons used = 100 / 40 = 2.5 imperial gallons. Litres used = 2.5 x 4.546 = 11.37 litres. Total cost = 11.37 x 145 = 1,648 pence = GBP 16.48. Cost per mile = GBP 16.48 / 100 = approximately 16.5 pence per mile. The critical distinction is the use of imperial gallons (4.546 litres) rather than US gallons (3.785 litres). Using the wrong conversion factor would underestimate your fuel cost by approximately 20%.