How to Calculate Fuel Costs
Whether you are planning a road trip, commuting to work, or comparing fuel types, knowing the cost of your journey helps you budget effectively. This calculator works with both miles per gallon (MPG) and litres per 100 kilometres (L/100km), making it suitable for UK and European vehicles.
How to Use This Calculator
- Enter your journey distance in miles or kilometres using the distance field and unit selector.
- Enter your fuel efficiency — either in MPG (UK gallons) or L/100km. You can find this in your car's manual or on the dashboard display.
- Set the fuel price per litre. The default is £1.45, but adjust it to match your local pump price.
- Tick "Include return journey" if you want to calculate the cost for a round trip. The calculator will double the distance automatically.
How It Works
The calculator first converts your distance to miles if needed, then calculates how many litres of fuel are required based on your efficiency. For MPG, it divides the distance by the MPG value and multiplies by 4.546 (UK gallons to litres). For L/100km, it converts the distance to kilometres and multiplies by the L/100km value divided by 100. The total litres are then multiplied by the price per litre to give you the journey cost. If the return journey toggle is selected, the distance is doubled before calculation. All processing runs locally in your browser — no data is sent to any server.
Frequently Asked Questions
How do I calculate fuel cost for a journey?
Divide the journey distance by your fuel efficiency (MPG or km/L) to get the amount of fuel needed, then multiply by the price per litre. For example, a 100-mile trip at 40 MPG uses about 11.36 litres, costing roughly £16.48 at £1.45 per litre.
What is the average fuel efficiency in the UK?
The average petrol car in the UK achieves around 36 to 40 MPG, while diesel cars typically achieve 40 to 50 MPG. Newer hybrid vehicles can exceed 55 MPG in mixed driving conditions.
How do I convert MPG to L/100km?
To convert UK MPG to L/100km, divide 282.481 by the MPG value. For example, 40 MPG equals approximately 7.06 L/100km. Our calculator handles both units automatically.
Does driving speed affect fuel cost?
Yes, driving at higher speeds significantly increases fuel consumption. At 70 mph a car uses roughly 9% more fuel than at 60 mph, and at 80 mph around 25% more. Keeping to 55-60 mph on motorways is the most fuel-efficient speed for most vehicles.
How much does a full tank of fuel cost in the UK?
A typical UK car has a 50-litre fuel tank. At £1.45 per litre, a full tank of petrol costs approximately £72.50. Diesel is usually slightly more expensive, costing around £75 to £80 for a full 50-litre tank.
Is diesel cheaper than petrol per mile?
Diesel engines are generally more fuel-efficient, so despite diesel often costing a few pence more per litre, the cost per mile can be lower for diesel vehicles, especially on longer motorway journeys. However, for short urban trips the difference is negligible.
