How the fuel cost calculator works
Last updated 10 November 2026
Fuel is usually the biggest running cost of a car. A quick sum of distance, consumption and price tells you what a trip or a month of driving costs.
How it works
- Litres = distance ÷ 100 × litres per 100 km.
- Cost = litres × price per litre.
Worked example
With the starting figures:
- The trip needs 37.5 litres.
- At the price shown, that costs R 900, or R 1.80 a kilometre.
How to read your result
The headline is the fuel cost for the distance you entered. With the starting figures the trip needs 37.5 litres and costs R 900. The cost for every kilometre divides that by the distance, so you can scale it to any trip.
The cost per kilometre only covers fuel. It does not include insurance, services, tyres or the loss in value of the car, so it is lower than the full cost of driving. The car ownership cost calculator adds those.
Finding your fuel use
The fuel use box takes litres for every hundred kilometres. The manufacturer publishes a figure, but real driving usually uses more. Your own records are usually closer to the truth.
To work it out yourself, fill the tank, reset the trip meter, drive as you normally do, then fill up again. Divide the litres you put in by the kilometres driven and multiply by a hundred. The fuel consumption calculator on this site does that sum for you.
What changes your fuel use
The same car can use quite different amounts of fuel from week to week. These things all push consumption up:
- Stop-start traffic and short trips.
- High speed on the open road.
- A heavy load, a roof rack or a trailer.
- Air conditioning.
- Tyres that are under-inflated.
Using it for a month or a long trip
For a month of driving, enter the kilometres you drive in a month. For a long trip, enter the full distance, and think about adding a margin. A tank rarely lasts to the exact litre, and detours add distance.
The fuel price in the starting example is not today’s price. Fuel prices change, so enter the price at the pump you will use. For a trip with tolls, food and accommodation, the road trip cost calculator covers the whole journey.
Common questions
Is the answer exact? No. It is an estimate based on the consumption figure you enter. Traffic, driving style and the state of the car all change the real number from trip to trip.
Can I split the cost between passengers? Yes. Divide the fuel cost by the number of people. The calculator does not do this for you, and it leaves out tolls, parking and wear on the car.
What about diesel or electric cars? For diesel, enter the diesel price. For an electric car, the petrol, diesel, hybrid and EV comparison tool works with kilowatt-hours and electricity prices instead.
Things to watch
- Traffic, speed, load and air conditioning raise consumption.
- A tank rarely lasts to the exact litre. Add a margin.
Planning a longer trip? Try the road trip cost calculator. Read the full disclaimer.