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 km i.e. divide 100 by km per litre
  • Convert km/litre to miles per gallon i.e. multiply km/litre by 2.825

Fuel conversion formula table

To convert Formula to use
km per litre to litres per 100 km divide 100 by km per litre
km per litre to miles per gallon multiply km per litre by 2.825
litres per 100km to miles per gallon divide 282.5 by litres per 100km
miles per gallon to litres per 100km divide 282.5 by miles per gallon
litres per 100km to km per litre divide 100 by litres per 100 km
miles per gallon to km per litre multiply miles per gallon by 0.354
km to miles multiply km by .62137
miles to km multiply miles by 1.6093
gallons to litres multiply gallons by 4.546
litres to gallons multiply litres by .21997

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

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