Calculating fuel consumption

Factors that can affect fuel consumption include:

• Lack of servicing
• Under-inflated tyres
• Air conditioning
• Roof racks
• Traffic density
• Air temperature
• Humidity
• The way the vehicle is driven

It's estimated 8% more fuel can be used on a return intercity trip when air conditioning is used for most of the journey. Therefore we recommend air conditioning is used sparingly.

We have also found the largest contributor to excessive fuel consumption is the way the vehicle is driven.

How fuel consumption is calculated

When we conduct tests the fuel tank is filled to the second click (i.e fill up the tank until the self-trigger "clicks off"). The trip meter is then zeroed and the vehicle is driven in urban and rural/highway environments (depending on the test we're undertaking). Cruise control is not used and typically, the distance travelled over the rural/highway test is 400 kilometres.

At the end of the test distance we refill the tank to the second click and note the distance and litres used.

Formulae used for conversion and calculation of fuel consumption:

• Divide the distance by the litres used to get the km/litre
• Convert the km/litre to L/100 kms i.e. divide 100 by kms per litre
• Convert km/litre to miles per gallon i.e. multiply km/litre by 2.825

Conversion formula table

Before you take action on your perceived high fuel consumption, we recommend you perform the fuel consumption tests twice compare the results.

More information

• 10 easy ways to save fuel
• Make cars green - 10 tips for greener driving
• Ask Jack your motoring questions