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The more you know about your electricity use, the more you can take control of your electricity costs. Here’s your guide to energy units, watts, kilowatt-hours and more.


What is a unit of energy?

An energy unit is how electricity use is measured. Each appliance in your home uses units of electricity – and you’ll be charged for the number of these energy units you use through your electricity bill.


A watt, a kilowatt and a kilowatt-hour

Watt, kilowatt and kilowatt-hours are energy terms you might come across as you learn more about energy units and your electricity usage.

Just as driving speed is measured in kilometres per hour, energy can be measured in watts and kilowatts and kilowatt-hours. Here’s a quick guide:

  • A watt (W) is a measure of power, or how fast energy is transferred. 
  • A kilowatt (kW) is one thousand watts, just like a kilometre is one thousand metres. This is a measure of power and can be used to show how much electricity an appliance might need to work. This is known as the appliances power rating. 
  • A kilowatt-hour (kWh) is a unit of energy which measures how many kilowatts are used in one hour. This is an important part of calculating your electricity bill.


The difference between a kilowatt and kilowatt-hour 

While a kilowatt refers to how much energy an appliance needs, kilowatt-hours measure how much electricity has actually been used over time. It can be helpful to think of a kilowatt-hour as how far that kilowatt of energy can get you, in the same way your driving speed is measured in kilometres per hour.

For example, it would take one kilowatt-hour of energy to run an appliance with a power-rating of one kW for one hour. If you ran that same appliance for two hours, you would be using 2kWh of electricity. 

Going back to the driving example, a kilowatt could represent your driving speed. Kilowatt-hours could represent how far you’ve driven – and this is what makes up the electricity usage you get charged for as part of your electricity bill.


How a unit of energy impacts your electricity bill

The number of energy units (or kilowatt-hours) you use – and how your electricity bill measures up to the average electricity bill for Perth – depends on a lot of different factors. These include:

  • The number of people who live in your house – The more people in your home, the more appliances, lights and heating and cooling you might use. 
  • Your appliances – If your appliances use a lot of power, this will add to your kilowatt-hours of use since you’ll use more electricity over time. On the other hand, energy efficient appliances will use less electricity compared to other models, which would mean these would use less energy units.
  • How you use your appliances – Some appliances use units of energy in standby mode, such as gaming consoles and microwaves. 
  • When you use your appliances – As an example, it's more efficient to heat or cool your house slowly over time, instead of cranking your heating on a cold morning or trying to cool your hot house quickly when you get home in summer.

Different appliances and electrical items contribute in different ways to the number of energy units you use. As a general guide, for an average household:

  • Heating and cooling makes up around 40% of energy use
  • Hot water accounts for around 25% of energy use
  • Appliances account for around 30% of energy use
  • Lighting is generally accounts for between 8% and 15 % of energy use

You can use our Electricity Bill Calculator to learn more about appliance running costs.


What is a unit of energy in terms of a Synergy bill?

When your electricity bill is calculated, your costs include the number of energy units you’ve used charged at the rate of your electricity plan. You can learn more about your electricity bill and see your electricity usage in My Account.

Let’s take using a fan heater as an example.
4 hours of using a 2000 watt (2kW) fan heater per day
4 hours x 2kw = 8 units of power

Then, these units of power are multiplied by the electricity rate in your plan.
If you have an A1 plan, this will be:
30.8120 cents x 8 units = $2.46 per day

Therefore, over a 60 day billing period, if you used the fan heater for 4 hours every day, this would make up around $147.90 of your electricity bill for your fan-heater, not including the daily supply charges and other electricity usage.

At Synergy, we don’t set the prices residential customers are charged for each unit of energy – this is set by the WA Government. However we calculate your bill based on information from your meter about how many units you have used. This data is provided to us by Western Power.

(Example is based on a 2000 watt upright fan heater during the relevant period applying the A1 tariff inclusive of GST as at July 2023 and excluding any other applicable charges.  The amount calculated is an estimated consumption cost only.  The actual charge may vary based on your applicable tariff, the particular appliance, the duration of use, the time of use, general conditions and appliance settings.  For up to date tariff information visit


Your electricity costs can change depending on your electricity plan

You could choose from a plan with one flat rate for every kilowatt-hour of electricity you use. This is known as our Home Plan (A1).

We also have electricity plans which may be available to you where you can be charged different rates based on when you use electricity. These are our Midday Saver and Electric Vehicle Add On plans, with a variable rate charging more at peak times and less at off-peak electricity times, such as during the day.


Explore our energy plans to find the right plan for you or get answers to common questions about electricity in WA.  

If you need help with your electricity bill, learn more about our payment plans, extensions and other ways we can help.