Trip Fuel Cost Calculator

Details

About this tool

Distance, consumption in litres per 100 km and the pump price give the fuel cost of a trip, the litres it will take, the cost per kilometre and the share per passenger.

The split is the point. Sharing fuel is the most common small settlement between people, and the arithmetic - a trip, a consumption figure, a price, divided by however many are in the car - is exactly the kind that gets estimated and then argued about. Having the number on screen ends the conversation. The return-trip toggle is there because that is the argument's other half: the driver is going home whether or not anyone else is in the car.

The consumption figure is where accuracy is won or lost. The manufacturer's number comes from a laboratory cycle and real driving beats it consistently - typically by 15 to 30 per cent, and by more in winter, in town, with a full car or a roof box. Cold starts are especially expensive, because the engine runs rich until it warms up, so a series of short trips can use half again what the same distance costs on a motorway. The honest input is your own long-run average from the trip computer or from receipts, not the brochure.

For an electric car the same structure works with different units: put consumption in kWh/100 km and the price per kWh. The result is then the cost of charging rather than of fuel, and the per-kilometre figure is directly comparable with the petrol one - which is usually the comparison people actually want.

Fuel is only part of what a kilometre costs. Tyres, servicing, depreciation and insurance add a substantial amount that this does not attempt to model, so treat the result as the marginal cost of the journey rather than the full cost of running the car.

Good to know

Questions people actually ask

My car is rated at 5 l/100 km but I never see it. Which figure should I use?

Yours. Manufacturer figures come from a standardised laboratory cycle and real driving typically uses 15 to 30 per cent more, with a bigger gap in town, in winter, or with a loaded car. Use the long-run average from the trip computer, or better, litres bought divided by kilometres driven over several tanks.

How do I convert MPG to l/100 km?

Divide 282.5 by the UK figure, or 235.2 by the US one - the two gallons differ. 40 UK mpg is about 7.1 l/100 km; 40 US mpg is about 5.9. Mixing the two up is a 20 per cent error, and neither figure carries a label saying which it is.

Does this work for an electric car?

Yes, with the units swapped: enter consumption in kWh/100 km and the price per kWh. You get the cost of charging, and the cost-per-kilometre figure is directly comparable with a petrol car's - which is the comparison most people are really after.

Why does city driving cost so much more?

Two reasons compound. Stop-start traffic wastes the energy spent accelerating every time you brake, and a cold engine runs rich until it warms up. A short trip can therefore use half again what the same distance costs on a motorway, which is why an average taken over mixed driving is more honest than one taken from a single long journey.

What does the per-person figure include?

Fuel only, split evenly across everyone in the car, with the return leg included if you tick it. It does not include tolls, parking, tyres, servicing or depreciation. That makes it the marginal cost of the trip - the right number for splitting fuel, not for pricing a car.