How to calculate your car’s fuel consumption

Calculating your car’s fuel consumption


With the petrol price continuing to rise, it is well worth it to know how to calculate your car’s fuel efficiency. If you know your fuel efficiency, you can budget more accurately, and you can also make some improvements to how you drive.


The following factors could affect your car’s fuel consumption:

  • Irregular servicing
  • Under-inflated tyres
  • Air conditioning
  • Traffic density
  • Air temperature
  • Humidity
  • The way you drive your car

According to the AA in New-Zealand, it is estimated 8% more fuel can be used on a return intercity trip when air conditioning is used for most of the journey. In hot summer months, this can most definitely affect your fuel consumption negatively, especially when you’re sitting in peak-time traffic.


Calculating your car’s fuel consumption

To make sure the numbers are as accurate as possible when calculating fuel consumption, follow these steps below:

  • Fill up your car until the self-trigger mechanism clicks (work from a full tank)
  • Zero your trip meter
  • Drive your car like you normally do - to work and back, on highways or arterial roads, etc.
  • Drive for around 400 km
  • Full up your tank again
  • Write down your distance travelled, and litres of fuel used.

Now, you’ll be able to calculate your car’s efficiency, based on how you normally drive.

  1. Divide the distance travelled by the litres used and you will get the km/litre
  2. Convert km/litre to L/100 km - divide 100 by km/litre

For the most accurate results, we recommend doing this test twice and comparing results, bearing in mind traffic flow, weather conditions, and if you made any changes to how you drive.