Guide · South Africa

What does fuel cost per kilometre?

One number tells you what every kilometre of driving really costs you in fuel. Here's the formula, a free calculator, and how to find your true figure.

The fuel cost per km formula

In words: take the price you pay per litre, multiply it by how many litres your car uses to travel 100 km, then divide by 100. The result is what one kilometre of driving costs you in fuel alone.

Worked example

Using example numbers (not current prices): fuel at R23.50 per litre and a car using 7.5 L/100 km:

• R23.50 × 7.5 = R176.25, the cost of driving 100 km
• R176.25 ÷ 100 = R1.76 per kilometre

Drive 1 000 km a month and that's about R1 762 in fuel, before any of your other running costs.

Cost per km by consumption level

Again with the example price of R23.50/L, your numbers will move these figures up or down:

Notice the pattern: at South African price levels, every extra litre of consumption per 100 km costs you roughly the price of one litre, spread over 100 km. Going from 7.5 to 9.5 L/100 km adds about R0.47 to every single kilometre at this example price.

Why your real cost per km differs from the calculator's guess

The formula is exact, but the consumption number you feed it usually isn't. Real-world consumption is pushed up by traffic and idling, air conditioning, vehicle load, short cold-engine trips, under-inflated tyres and aggressive acceleration. For e-hailing drivers, dead kilometres, driving to a pickup or repositioning with no passenger, are distance you pay for out of your own fuel but don't earn from.

How to find your true consumption in one tank

1. Fill the tank and write down the odometer reading (or reset your trip meter).
2. Drive as you normally would.
3. At the next fill-up, note the litres pumped and the kilometres travelled.
4. Real consumption = litres ÷ kilometres × 100.

One tank gives a decent estimate; three or four tanks give a figure you can trust.