With the current price of petrol, we're all being that little more cautious when we drive. Aside from the monthly instalments on a financed car, the monthly fuel bill is often the second-highest cost we will incur while owning a car. Yup, even insurance works out cheaper; at this rate, a single full tank costs more than the average insurance instalment.
We're all trying to save fuel and some of us are on the hunt for a more fuel-efficient car, but before we go down this route we need to know how bad the current situation is.
Related: How to improve fuel economy
Simply put, the average fuel consumption of your car is a calculation of how many kilometres you were able to travel for every litre of fuel used, be it diesel or petrol. Some vehicles will help you out by calculating your averages and sometimes even give you an instantaneous reading of how much fuel you are using. In order to understand how these readings affect you, we need to start with the units of measurement.
Units of measurement
Fuel consumption is most commonly quoted as litres per 100 kilometres condensed to read as "l/100km". A more traditional way of measuring it is kilometres per litre expressed in "km/l".
Both of these give a similar indication of the amount of fuel used and l/100km is more common because the lower the number, the better the fuel consumption of the vehicle - remember, using less fuel is better!
The longer you drive, the more information the car has to be able to work out your average fuel consumption. Steady driving uses less fuel than stop-start driving and the amount of time or kilometres you spent in these situations is reflected in your average fuel consumption. Driving erratically, accelerating hard and stopping suddenly all negatively affect your fuel consumption.
If you travelled 10 kilometres and used 1 litre of fuel, your car has an average fuel consumption of 10 km/l or 10 l/100km. Similarly, if you travelled 10 km and used 2 litres of fuel, your car did 5 km/l. 10 ÷ 2 = 5. This is equal to 20 l/100km when converted.
10 is the magic number and the crossover point for the conversion between km/l and l/100km.
How is it calculated?
In simple terms, your vehicle will compare the kilometres you've travelled and compare it to how much fuel you've used to do those kilometres. It's then expressed in the units listed above as average fuel consumption.
If you happen to have a vehicle that is a little older and doesn't have a readout for fuel consumption you can work it out yourself. Here's what you do:
- Fill your car with fuel, the first click of the nozzle is fine.
- Reset your trip meter or make a note of your odometer reading.
- Drive your car as you normally would. You can do this as you go about your regular routine, it doesn't need to be anything special.
- Fill the car again (to the same point as before ie: first click) and take note of two things before leaving the garage: the trip meter/odometer reading and the number of litres you had to put in to fill the car again.
You now have the two figures you need to do the calculation. Divide the number of kilometres by the litres of fuel you topped up with. This will give you the fuel consumption of your car in km/l.
If you wish to convert this to l/100km, divide 100 by the number you got for km/l.
Example:
60 km travelled
5 litres of fuel used
Equals: 12 km/l
To convert to l/100km:
100 ÷ 12 = 8.33
Equals 8.33 l/100km
Keep track of these numbers as you go and figure out what sort of driving you were doing to see what routes or driving styles are negatively affecting your fuel consumption. Remember to get that car serviced! It's one of the biggest causes of poor fuel consumption.
