Calculate the exact fuel cost of any journey or your total monthly fuel spend — instantly.
This calculator uses your journey distance, vehicle fuel efficiency (MPG), and current fuel price per litre to calculate the exact cost of any journey. It converts miles per gallon to litres per 100km internally to give you an accurate cost in pounds.
The formula used is: Fuel cost = (Distance ÷ MPG) × 4.546 × Price per litre. For example, a 100-mile journey in a car achieving 40 MPG with petrol at £1.48/litre would cost approximately £16.80.
Fuel prices in the UK vary by region and retailer. As a guide, average UK fuel prices in early 2025 are approximately £1.48/litre for unleaded petrol and £1.54/litre for diesel. Supermarket forecourts are typically 3–5p per litre cheaper than motorway services.
The average fuel efficiency for a petrol car in the UK is around 36–40 MPG in real-world driving. Diesel cars typically achieve 45–55 MPG. Hybrid vehicles can reach 50–70 MPG, and newer electric vehicles are measured in miles per kWh rather than MPG.
To convert from L/100km to MPG (UK), use the formula: MPG = 282.48 ÷ L/100km. For example, a car using 7 litres per 100km achieves approximately 40 MPG. Our calculator accepts MPG directly, which is the standard measurement used in the UK.
The calculator uses a single MPG figure for the whole journey. For more accuracy, use your real-world combined MPG rather than the manufacturer's quoted figure, which is typically measured under ideal conditions and can be 15–20% higher than real-world performance.