Fuel Costs & Calculations Cost Calculator

How to calculate fuel cost?

CheckFuelPrices Editorial Expert Written • 4 industry sources

Reviewed by Jonathan Mathews VERIFIED

LinkedIn Articles 5+ Yrs Peer Reviewed

To calculate fuel cost, divide your journey distance (in miles) by your car's MPG, then multiply by the price per gallon (price per litre × 4.546). Getting the fuel price right is just as important as knowing your MPG — even a 5p per litre difference adds up significantly over time.

The Basic Fuel Cost Formula

Core formula: Fuel cost = (Distance in miles ÷ MPG) × (pence per litre × 4.546 ÷ 100). The 4.546 converts litres to imperial gallons, and dividing by 100 converts pence to pounds.

Worked example: A 200-mile trip in a car doing 40 MPG, with fuel at 140p per litre: (200 ÷ 40) × (140 × 4.546 ÷ 100) = 5 × 6.364 = £31.82.

Metric alternative: If your car shows L/100km, the formula is: (Distance in km ÷ 100) × litres per 100km × price per litre (in pence) ÷ 100.

Finding the Right Fuel Price

Prices vary widely by station: UK pump prices can differ by 10p or more per litre between the cheapest and most expensive stations in the same area, so using an accurate local price matters. 3

Use live data: CheckFuelPrices pulls from CMA government open data and updates every 30 minutes, giving you the real pump price at 4,000+ stations rather than a national average. 1

National averages as a benchmark: DESNZ publishes weekly average UK petrol and diesel prices, which are useful for broad estimates but may not reflect what you'll actually pay locally. 2

Calculating Annual or Monthly Fuel Spend

Annual cost: Multiply your weekly mileage by 52 to get annual miles, then apply the formula above. The average UK driver covers around 7,400 miles per year. 3

Petrol vs diesel comparison: When comparing petrol and diesel running costs, you need to factor in both the MPG difference and the price-per-litre difference — diesel is typically 3–5p more expensive but more efficient. 4

MPG from your car: Use the official combined MPG from your vehicle's spec sheet as a starting point, but real-world MPG is typically 15–20% lower depending on driving style and conditions.

Reduce Your Calculated Cost

Find the cheapest station on your route: Once you know your fuel cost formula, reducing the price per litre is the quickest lever. Even saving 5p per litre saves £2.27 per tank on a 45-litre fill. 1

Supermarkets are consistently cheaper: Tesco, Asda, Sainsbury's, and Morrisons typically undercut branded stations by 3–8p per litre. CheckFuelPrices lets you compare them all in one search by postcode or town. 1