About the Fuel Cost Calculator
This fuel cost calculator estimates what a journey will cost in petrol, diesel or electricity from three inputs: distance, your vehicle's efficiency and the current price per unit. It also reports the fuel volume needed and the cost per unit of distance, which is the figure worth remembering when deciding between driving and taking the train. Tick the return trip box to double the distance, and set the number of people to divide the cost evenly for a car share. The maths works in metric or imperial as long as your units are consistent.
How to use the Fuel Cost Calculator
- 1
Enter the Distance for one leg of the journey, in kilometres or miles.
- 2
Enter your Fuel efficiency in the matching unit — km per litre if you used kilometres, miles per gallon if you used miles.
- 3
Enter the Price per litre or gallon you expect to pay.
- 4
Set 'Split between' to the number of passengers sharing the cost.
- 5
Tick 'Return trip' to double the distance, then read the total cost, fuel needed and per-person share.
What people use it for
Planning a road trip budget
A 500 km leg in a car doing 15 km per litre at 105 per litre needs about 33.3 litres and costs roughly 3,500. Tick the return box and it doubles to around 7,000.
Splitting costs on a car share
Four people sharing a long drive can see the exact per-head figure, which makes for a cleaner conversation than a rough guess at the petrol station.
Driving versus public transport
The cost per unit distance gives a clean comparison against a rail or coach fare, though remember fuel is only part of the true cost of driving.
Keeping the units straight, including for electric cars
The calculation is fuel = distance ÷ efficiency, then cost = fuel × price. Nothing in it knows what units you are using, so consistency is entirely on you. Kilometres pair with kilometres per litre and a price per litre. Miles pair with miles per gallon and a price per gallon — and you must use the same gallon as your economy figure. To move between systems: multiply US miles per gallon by 0.425144 to get kilometres per litre, or imperial mpg by 0.354006. Going the other way, multiply km per litre by 2.35215 for US mpg or 2.82481 for imperial. Europe usually quotes consumption inverted as litres per 100 km, which is not a direct multiplier at all — convert with km per litre = 100 ÷ (litres per 100 km), so 6.5 L/100 km is 15.4 km per litre. For an electric vehicle the same arithmetic works untouched: enter efficiency as kilometres per kilowatt hour, typically 5 to 7 for a modern car, and price as your cost per kWh.
Why the real bill usually comes in higher
Manufacturer economy figures come from standardised laboratory cycles, and real-world driving reliably falls short. Speed is the biggest single factor, because aerodynamic drag rises with the square of velocity: sustained motorway driving at 110 km/h can use 15 to 20 percent more fuel than the same route at 90. Stop-start urban traffic is worse still, since every acceleration throws away the energy that braking then dissipates as heat. Cold weather hurts twice, through a longer warm-up on a rich mixture and denser air, and short journeys on a cold engine can double consumption per kilometre. Air conditioning typically adds 5 to 10 percent, a roof box or bike rack can add 10 to 25 percent at speed, and tyres 20 percent under-inflated waste around 2 to 3 percent. A fully loaded car with four passengers and luggage burns noticeably more than the same car driven alone. Electric vehicles are affected by cold most of all, often losing 20 to 30 percent of range in winter. Treat the result as a planning estimate and add a margin of at least 10 to 15 percent for anything you are budgeting tightly.
Tips
- Work out your own real efficiency by filling the tank, resetting the trip meter, and dividing the distance covered by the litres taken at the next full fill.
- Fuel is only part of the cost of driving; tolls, parking, tyre wear and depreciation typically add as much again on a long trip.
- For a fair comparison with public transport, price both door to door rather than station to station.