Fuel Cost Calculator
Calculate the fuel cost of any journey. Enter your distance, fuel economy and fuel price to see litres used, total trip cost and cost per mile.
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How the fuel cost calculator works
The calculator converts your journey and fuel economy into litres used, then multiplies that by the fuel price you enter. It supports UK MPG, US MPG, litres per 100 km and kilometres per litre.
It is useful for commuting, road trips, motorhomes, vans and comparing the likely running cost of two vehicles.
Quick formulas
- UK MPG → litres: miles ÷ MPG × 4.54609
- US MPG → litres: miles ÷ MPG × 3.78541
- Cost: litres × price per litre
- Cost per mile: total cost ÷ miles
How to measure your real MPG accurately
For a real-world MPG figure, use the full-to-full method. You do not need to know exactly how many litres are in the tank. You only need to refill to the same point each time and record the fuel added.
- Fill the tank consistently. Use the same pump orientation if practical. Fill until the nozzle clicks off, pause briefly, then continue until it clicks off a second time. Do not keep repeatedly topping up beyond that point.
- Reset the trip counter or note the vehicle odometer reading.
- Drive normally. A longer distance gives a more representative result than a short trip.
- Refill using the same method. Fill to the first click, pause, then to the second click again.
- Record the litres added and miles travelled. The litres put back in are approximately the litres used since the previous full tank.
For best accuracy: calculate over several full tanks and average the results. Pump shut-off sensitivity, vehicle angle, temperature and how quickly you fill can move a single-tank result slightly.
Frequently asked questions
What is the most accurate way to calculate my real MPG?
Use the full-to-full method: fill to a consistent nozzle shut-off point, reset the trip counter, drive, then refill to the same shut-off point. Divide the miles travelled by the UK gallons represented by the litres added. Averaging several tanks reduces filling variation.
Is UK MPG different from US MPG?
Yes. An imperial gallon is larger than a US gallon, so the same car produces a higher numerical MPG figure when measured using UK gallons.
How accurate is the result?
The calculation is exact for the values entered. Real fuel use varies with traffic, speed, weather, tyre pressure, vehicle load and driving style.
Can I use this for a motorhome or campervan?
Yes. Use the MPG you actually achieve when loaded rather than a brochure figure.
Can I compare petrol and diesel?
Yes. Run the calculation once for each vehicle using its own fuel economy and current fuel price.