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I often wonder how much energy a given item in my home is using. Examples include:

  • the clock on my microwave
  • my espresso maker
  • an electric water kettle
  • my phone charger (when no device is attached)
  • the garage door
  • my NES
  • the dehumidifier in the basement

How should one go about finding out (or estimating how much electricity a given household item uses?

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    There are loads of power monitors on the market. Some should be installed on your main electricity meter and only show differences between total usage. Others you can just plug-in between the device and the socket in the wall to measure what that device uses. More info also in this article on Treehugger or check this list of over 350 monitors on Amazon – THelper Aug 4 '15 at 12:41
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The easiest way is to buy a meter that plug into the power outlet and the device you want to measure is plugged into the meter. Something like this:

Power meter

Depending on the meter you buy, it will measure watt of power used and kWh, as well as other measures of power consumption/utilization.

Such meters are available at most major hardware or electrical stores.

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    Make sure you buy one that is simple. They sometimes have all kinds of bells and whistles (e.g. like calculating the amount of money this will cost) that make them difficult to use. There is basically one measurement you need: average power consumption (maybe split over different tariff periods). Any subsequent calculations you can do on the back of en envelope. – Jan Doggen Aug 7 '15 at 13:21
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One method, which is not very accurate but is very easy, is to look on the back. Most appliances, or their power supplies if seperate, will have this info printed on their back. In some cases (e.g. Simple appliances such as An electric heater or tumble dryer) this will be the power that they actually use, and in some (eg a computer) it will be the maximum rating of the power supply, and thus only an upper limit that may never be reached.

Sometimes the power is given in watts. Sometimes, instead, the current draw is given in amps (A) or milliamps (mA) (there are a thousand milliamps to an amp). In this case, multiply the current by the voltage where you are to get the power [1]. For example, most of Europe has mains electricity at 230V, so if the label said "input: 200mA" you would do 0.2 × 230 = 46W.

Having said all this: for many purposes, you are much better off with a meter :-)

[1] for the pedants, I'm deliberately ignoring power factor. Most domestic electricity meters ignore it too.

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