Fuel cost is the distance ÷ your car's mileage × the price of fuel: 300 km at 15 km/l and 100 a litre costs 2,000, or 500 each for four people. Choose km/l or mpg, add a round trip, and the cost is split for you.
The formula
Fuel used
fuel = distance ÷ mileage (distance × 2 for a round trip)Trip cost
cost = fuel × price per litre or gallonPer person
per person = cost ÷ peopleEach km or mile
cost per km or mile = price ÷ mileageA US gallon is 3.785 litres and an imperial gallon is 4.546 litres, as the NIST Guide to the SI lists them. The calculator works in whichever unit you choose, so the price must be per the same litre or gallon.
Worked example
Going and coming back doubles it: 600 km needs 40 litres and costs 4,000, or 1,000 each.
When to use it, and the mistakes to avoid
Use it to budget a road trip, to share the petrol with friends or colleagues on a lift, or to compare driving with other ways of travelling.
- Using the maker's mileage. Use what your car really gets.
- Mixing units. Kilometres go with km/l and a price per litre; miles go with mpg and a price per gallon.
- Forgetting the way back. Switch on round trip for a return journey.
- Ignoring tolls and parking. They are not included.
- Treating the shares as exact. Each share is rounded to the cent, so they can differ from the total by a cent.
FAQ
How do I calculate the fuel cost of a trip?
Divide the distance by your car's mileage to get the fuel used, then multiply by the price of fuel. 300 km at 15 km/l is 20 litres, and at 100 a litre that is 2,000. Add the people sharing and the calculator divides it for you.
What is the difference between mpg (US) and mpg (UK)?
The gallon. A US gallon is about 3.785 litres and an imperial (UK) gallon about 4.546 litres, roughly a fifth bigger, so the same car gets a higher mpg on the UK scale. Pick the one your figure or your fuel price uses, and enter the price per that gallon.
How do I change km/l to mpg?
Multiply km/l by 2.352 for US mpg, or by 2.825 for UK mpg. So 15 km/l is about 35.3 mpg (US) or 42.4 mpg (UK). You do not need to convert here: choose the unit you have and enter the distance in kilometres or miles to match.
Which mileage should I use?
The one you really get, not the maker's figure. Fill the tank, reset the trip meter, drive as you normally do, then divide the distance by the fuel you put in at the next fill. City driving, a full boot and a roof box all lower it, and steady motorway driving at moderate speed usually raises it.
Does it include tolls, parking and wear?
No. It is fuel only. Add tolls, parking and any other costs of the trip yourself before you split it, and remember that wear, tyres and servicing also rise with distance. The per-km figure shown is the cost of fuel alone.