How to Use the Fuel Cost Calculator
The Fuel Cost Calculator computes the cost of any journey — or your monthly and annual fuel bill — based on your vehicle's fuel efficiency and current fuel prices. It works in both imperial (MPG, miles) and metric (L/100km, kilometres) units.
Enter the distance of your trip or monthly mileage, your vehicle's fuel economy (mpg or L/100km), and the current fuel price per litre or gallon. The calculator shows the total fuel cost and lets you compare the running costs of different vehicles side by side.
An important nuance is the difference between manufacturer-stated MPG and real-world efficiency. Official WLTP figures are typically 20–30% better than what most drivers achieve. Use your actual average fuel economy (calculate from fill-ups) for accurate cost projections.
📊 Worked Example
100-mile commute in a car getting 35 MPG real-world, petrol at £1.55/litre:
- Fuel for trip: 2.86 gallons / 13 litres
- Trip cost: £20.15
- Monthly (20 commutes): £403
- Annual fuel cost: £4,836
Common Use Cases
- ✅ Calculating the fuel cost of a road trip before you set off
- ✅ Comparing running costs of different vehicles before buying
- ✅ Working out monthly fuel spend to budget accurately
- ✅ Comparing driving vs train/bus costs for a regular commute
- ✅ Evaluating whether an electric vehicle would save money vs petrol
- ✅ Calculating fuel costs for a business mileage expense claim
- ✅ Seeing the annual cost of fuel at different efficiency levels
Frequently Asked Questions
How do I calculate fuel cost for a trip?
Fuel cost = (distance ÷ fuel economy) × price per unit. For example: 150 miles ÷ 35 MPG = 4.29 gallons × £1.55/litre (convert gallons to litres: × 4.546) = £30.17. Our calculator does this instantly in any unit combination.
What is the difference between MPG and L/100km?
MPG (miles per gallon) measures how far you travel per unit of fuel — higher is more efficient. L/100km (litres per 100 kilometres) measures how much fuel you use per unit of distance — lower is more efficient. To convert: divide 282.5 by MPG to get L/100km.
What MPG should my car get?
Average fuel economy by vehicle type (real-world): small city car 40–50 MPG, family saloon 35–45 MPG, SUV 25–35 MPG, large SUV/4x4 20–30 MPG, van 25–35 MPG. Hybrid vehicles can achieve 50–70+ MPG in mixed driving.
How can I improve my fuel economy?
Key improvements: maintain correct tyre pressure (under-inflation costs 2–3% MPG), remove excess weight, drive smoothly (avoid harsh acceleration/braking), use cruise control on motorways, don't idle unnecessarily, and service the engine regularly (air filter, spark plugs).
How does petrol price affect my annual fuel cost?
A 10p/litre rise in petrol costs about £73 extra per year for a typical driver doing 8,000 miles at 35 MPG. For a van driver covering 25,000 miles at 30 MPG, the same 10p rise adds £379/year. Use the calculator to model your specific scenario.