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    How is Electricity Measured?

July 2019

Want to know what’s what when it comes to how many watts your appliances use? Learn how to compare the power consumption of different appliances and take control of your energy bill.

Using less electricity around the home is a great way to reduce your energy bill and do your bit for the environment, but if it’s dark we need to switch the lights on, right? It could be easier for you to reduce your electricity consumption by learning how electricity is measured and used in different appliances.

Watts and their big siblings kilowatts, megawatts and gigawatts are the most common units of measurement for electricity. You can use these units to gauge how much energy an appliance may consume, which in turn is useful if you want to take control of your power use and your energy bills.

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 appliances use different amounts of power. Refrigerators, televisions, washing machines and toasters all use different amounts of energy, as do old-style incandescent light globes versus their modern, energy-efficient equivalents.

To understand how much power different appliances use – and how to modify usage to reduce your electricity use – we need a common system that rates everything we plug in and turn on.

That’s where the useful composite measurement: “watts per hour” (Wh) or “kilowatts per hour” (kWh) come in1. Most devices that are powered by electricity should include information about their average watts per hour of energy consumption.

Comparing power use

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.

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.

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, 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).

The final word

Understanding how many watts per hour your appliances use might help you adjust how or when you utilise them – which could help reduce your energy bills. To learn more about the power consumption of different appliances around the home, read our guide on How Much Energy do Household Appliances Use?

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