Your gas meter measures gas usage in cubic meters, but in most states your usage is actually billed in ‘megajoules’ (MJ) on your bill. In WA only, usage is measured in 'units'. A unit of gas is equivalent to 1 kilowatt hour of energy. To determine units, the number of megajoules is divided by 3.6.
To calculate the number of megajoules you've used in a billing period, AGL first subtracts the start read on your meter from the end read, and then multiplies the result by two values - the heating value and pressure factor.
Both of these values are provided to us by your local gas Distributor - the company responsible for reading your meter and maintaining the pipes in your area. Heating value and pressure factor vary based on local conditions at different geographical locations, such as temperature, pressure and the appliance consuming the gas.
All of the values used in these calculations are shown on the last page of your gas bill. Here's an example of how they look:
And the calculations using these example numbers:
( End read - Start read ) x Heating value x Pressure factor = Usage MJ
( 229 - 220 ) x 38.6336 x 1.0272 = 357.15
The supply charge also known as the service charge (or service to property charge), is the charge that applies for supplying electricity to your premises for each day of the billing period, regardless of how much electricity you use.
Electricity daily supply charges may vary depending on the electricity network region you are connected and what type of tariff you are on.
Supply charges are generally calculated as a contract term amount charged for each day of the time period covered by a bill. They are not related to the amount of energy used during the billing period.
Supply charges cover some of the costs of maintaining and operating the Distribution and Transmission networks (see explanation of Network Costs), and some of the operational costs of supplying our customers.
To arrive at the supply charge on your bill, we multiply the daily rate by the number of days your energy is supplied.
Your gas meter shows gas usage in cubic meters whereas usage on your bill is shown in Usage Units.
To determine your gas usage in Units, the following calculation is performed:
Usage units = ((End read - Start read) x Pressure Factor x Heating value)/3.6 = Usage (MJ)
While this is a common formula used to calculate your gas usage in megajoules, it can vary slightly depending on the type of gas meter you have at your property.
The Pressure Factor and Heating Value are used to convert the metered gas volume you have used into an amount of energy calculated in megajoules.
A unit of gas is 3.6 megajoules and is equivalent to 1 kilowatt hour.