calculating your electricity usage

electricitymeterSince looking at calculating the saving of turning out lights, I got a bit obsessive with calculating the cost of running various appliances in our house. It can be quite surprising how much certain appliances cost to run.

Knowing how much electricity that you’re using each day, what your consumption patterns are and what appliances cost the most is the first step in reducing your electricity bill.

To track your electricity usage, you could buy a wireless power monitor. If you’re in QLD, for $50 you can have an electrician come to your home and assess your electricity usage, give you a wireless metre, 15 light globes and a shower head through the Climate Smart Home.

However, it can be quite simple to calculate your electricity usage without the fancy devices.

Start by reading your metre everyday (or more or less depending how keen you are) and keep a record or chart your usage, keeping in mind what appliances you use during the day. You will have usage spikes on the days that you run the washing machine or use the air conditioner, for example.

Reading the metre and tracking electricity usage day by day means that you can immediately observe the effects of the changes that you make to reduce the amount of electricity that you use, without having to wait for the next bill. Make reading the metre and reducing consumption a competition with the family to get everyone involved.

Living in a townhouse, our electricity metre is behind lock and key, so we don’t read our metre (although I would like to do the exercise). For instructions on how to read your electricity metre, see the article on the Down to Earth Blog.

Reading your metre only gives an indication of your electricity consumption overall. To work out how much electricity each appliance consumes and how much each appliance costs you, you need to calculate the kilowatt usage for each. There are several methods for doing this.

Firstly, many appliances give you an indication of how many kilowatts per year the appliance uses. You will find this information on the energy rating sticker. The appliance for the sticker below uses 505 kilowatts a year. According to our electricity bill we pay $0.17130 per kilowatt hour, so this appliance would cost us $86 per year or $0.23 per day to run. 


Apart from the energy rating sticker, most appliances have their wattage printed somewhere on them so you can work out how much they cost to run. A simple equation to work out how much running an appliance costs you:

Wattage x hours used per day / 1000 = daily kilowatt usage

(1 kilowatt hour = 1,000 watts)

As an example, our kettle takes 2,200 watts to run. Assuming that I boiled it (full) for a total of 1/2 hour per day it would use 1.1 kilowatts per day.

To work out the cost, multiply the kilowatts per day by the cost per kilowatt hour as per your electricity bill.

According to our latest electricity bill, our electricity costs $0.17130 per kilowatt hour. So at 1/2 hour per day, it costs us 19c each day to boil the kettle.

To calculate the usage per year, multiply the daily kilowatt usage by the number of days the appliance is used per year.

To boil the kettle, over a 365 day year that is 401.5 kilowatts (365 x 1.1 kilowatts)

To calculate the cost per year, multiply the yearly kilowatt usage by the cost per kilowatt hour as per your electricity bill.

In total, $68 per year to boil the kettle (401.5 x $0.17130)

If your appliance only has the amps printed on it, times the number of amps by the voltage (240 volts in Australia, 120 volts in the US) to get the wattage, ie 6 amps x 240 volts = 1,440 watts.

Alternatively, if you don’t have the wattage, you could get an estimate of the wattage online for that appliance.

Calculating the cost of using appliances isn’t an exact science but it gives you a good idea what appliances consume the most electricity and which ones cost the most. Calculations are based on maximum output, so if you run your heater on a lower setting for example, it uses less wattage.

The first step in reducing electricity consumption is having an idea of how much you are currently consuming and your consumption habits – whether it’s boiling the kettle every hour :) or whether Saturdays are your biggest consumption because the kids are home. Once you are aware of your current consumption habits, it becomes easier to choose the habits to change that will have the biggest impact on reducing your electricity bill.

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  1. Peter says

    Great article, I have been wondering how to calculate energy cost. now I no longer have to wonder how.