How is electricity measured?

What is a watt?

Fun fact: the watt was named after steam engine inventor James Watt. For the technically minded, a watt equates to the energy consumption rate of one joule per second. For the rest of us, it’s enough to know that a watt is a way to measure the amount of electricity we use.

Different power usages

Different appliances use different amounts of power. For example:

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  Refrigerators: These typically use between 100 to 800 watts depending on their size and efficiency.

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  Televisions: Modern LED TVs use around 60 to 150 watts, while older CRT models use more.

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  Washing machines: These can use anywhere from 400 to 1300 watts.

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  Toasters: A typical toaster uses about 800 to 1500 watts.

Comparing these figures can help you understand which appliances are the biggest energy consumers in your home.

What is a watt-hour?

A watt-hour is the amount of energy used by a device that consumes one watt of power over the course of one hour. For example, if you leave a 100-watt light bulb on for one hour, it will consume 100 watt-hours of electricity.

What is a kilowatt-hour?

A kilowatt-hour (kWh) is 1,000 watt-hours. This is the unit you’ll most often see on your electricity bill. It represents the total amount of energy used. For instance, if you run a 1,000-watt appliance for one hour, you’ve used 1 kWh of electricity.

If you look at the back of your TV or inside the door of the fridge, you’ll see a panel with lots of fine print. Sometimes, the electricity measurement units will be written in watts (W or Wh) on this panel.

More often though, you’ll need to do some simple maths to understand how much power the appliance is using. It’s typical for appliances, including power adapters, to show their volts (V) and amps (A). Get out the calculator: the watts-per-hour amount is simply the volts multiplied by the amps2.

Example calculation: Let’s say your refrigerator states it uses 120V and 5A. To find out how many watts it uses:

Watts = Volts × Amps Watts = 120V × 5A = 600W This means your refrigerator uses 600 watts of power.

Side note: Light globe ratings are just a shortcut to saying watts per hour, so a 10W globe uses 10 watts of power per hour.

Managing energy consumption

Once you’ve got an understanding of how much power your appliances use, you can consider ways to minimise the cost of using high-energy appliances. For example, if your type of tariff permits, you might want to use a high-energy appliance like a clothes dryer during an off-peak period, or when the sun is feeding power into your solar panels (if you have them). Refer to How to make the most of off-peak electricity times for more information.

Here are a few of our top tips to reduce energy consumption in your home:

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  Use energy-efficient appliances: Choose appliances with higher energy star ratings. They might cost more upfront but save money in the long run. To learn more about the power consumption of different appliances around the home, refer to A guide to understanding household appliance power usage for more information.

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  Unplug unused devices: Many devices continue to draw power even when turned off. Unplugging these can save energy.

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  Use power strips: Grouping devices on a power strip makes it easier to switch them all off at once.

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  Adjust thermostat settings: Lowering your thermostat in winter and raising it in summer can significantly reduce energy use.

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  Regular maintenance: Ensure appliances like refrigerators and air conditioners are well-maintained to operate efficiently.

The final word

Understanding how electricity is measured and the wattage of your appliances can empower you to make informed decisions about their usage. By adjusting how and when you use them, you can effectively lower energy bills, positively impacting your household budget.