Fuel Cost Calculator
Work out how much a journey will cost in fuel. Enter your distance, your car's fuel efficiency, and the current fuel price — results show total litres, total cost, and cost per mile or km.
How Fuel Cost Calculator works
MPG and the imperial gallon
UK fuel efficiency is traditionally quoted in miles per gallon (MPG), where the gallon is the Imperial gallon of 4.54609 litres. To convert MPG to litres needed: multiply the distance in miles by 4.54609 (litres per gallon) and divide by the MPG figure. For example, a 150-mile journey in a car that does 40 MPG uses (150 × 4.54609) ÷ 40 = 17.05 litres.
L/100km (European efficiency standard)
European car manufacturers typically rate fuel efficiency in litres per 100 kilometres (L/100km). To convert: divide the distance in km by 100, then multiply by the L/100km figure. For example, 150km at 6.5 L/100km = (150 ÷ 100) × 6.5 = 9.75 litres. Lower L/100km is more efficient; higher MPG is more efficient. To convert MPG to L/100km: 282.48 ÷ MPG.
Fuel price and forecourt costs
Fuel prices in the UK are quoted per litre and vary by region, forecourt, and market conditions. Motorway services typically charge 10–15p more per litre than supermarket forecourts. The default rate used here (145p/litre) is approximate and changes frequently. Always check the current price at your local forecourt for an accurate calculation.
Actual vs manufacturer-quoted efficiency
Real-world fuel economy is typically 15–25% worse than the official WLTP test figures due to driving style, load, route, climate, and tyre condition. Motorway driving at constant speed tends to be more efficient than urban stop-start. If your car is due a service, low tyre pressure or a dirty air filter can significantly reduce efficiency.
Frequently asked questions
How do I calculate the fuel cost of a journey?
Divide the distance (in miles) by your MPG to get gallons used, then multiply by litres per gallon (4.54609) to get litres. Multiply litres by the price per litre to get the total cost in pence, then divide by 100 for pounds. This calculator does all of this automatically.
How do I convert MPG to L/100km?
To convert MPG to L/100km, divide 282.48 by the MPG figure. For example, 40 MPG = 282.48 ÷ 40 = 7.06 L/100km. To convert L/100km to MPG, divide 282.48 by the L/100km figure.
What is the average MPG for a UK car?
The average new car sold in the UK achieves around 45–55 MPG under WLTP test conditions, though real-world figures are lower. A petrol family hatchback typically achieves 35–45 MPG in real-world driving. Diesel cars are generally 15–25% more efficient than equivalent petrol models; hybrids can achieve 50–70+ MPG.
How can I improve my fuel economy?
The most effective changes are driving at steady speeds (60–65 mph is typically the most efficient for most cars), avoiding harsh acceleration and braking, maintaining correct tyre pressure, removing unnecessary weight (roof boxes, heavy loads), and keeping the engine serviced. Removing roof bars and boxes when not in use saves around 10–15% at motorway speeds.
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