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How to Use a “Kill A Watt” Energy Meter

Want to test your household appliances to see how efficient they really are? 

A Kill A Watt Energy Meter allows you to safely and accurately measure the power consumption of household appliances. You can check the amps, volts, and even see the cumulative consumption of your appliances by kilowatt-hour (kWh), which is the measurement your utility company uses on your bill.  

This tool exposes those dreaded vampire loads around your house.  A vampire load is an appliance that uses energy even when they’re “turned off.”  Some of the main energy-sucking culprits in your home could be the microwave, PC, coffee maker, or television. You could have a number of these vampire loads running 24/7, costing you hundreds of dollars every year.  Anything with a digital clock is a suspect, so let’s learn how to test an appliance!

This little gadget will make it easy to determine what’s costing you the most. You can set the Kill A Watt Energy Meter to measure the cost of running an appliance by adjusting this energy meter to a rate(s) that’s comparable to what your utility company charges per kWh.

The Kill A Watt Energy Meter is particularly helpful for estimating the amount of energy used by appliances that cycle.  I decided to plug our refrigerator into the Kill A Watt to see just how much energy it draws.

Step 1. Plug it in

To get started, plug your appliance directly into the Kill A Watt and then plug your Kill A Watt into the AC wall outlet. 

Currently drawing 118.8 Volts

Now you can reference the Kill A Watt’s LCD display to see the voltage (Volts) and current (Amps).  In addition to volts and amps, it’ll show you Watts (which is volts x amps), and frequency in Hz.  

Over time, the Kill A Watt will rack up kilowatt-hours.  To get an idea of how much it costs to run my fridge, I have the rate set at $0.25 per kWh.   I’m presupposing that that I pay my utility company a quarter for every kilowatt-hour I use.


Step 2. Check the Clock

You might want to take a note of the time you plugged it in, even though it will tally the hours that it’s connected.  

Come back in a day, a week, or whenever.


Step 3. Write it Down

Once the Kill A Watt has been plugged in for a while, you can read the sum of the energy your appliance consumed in kilowatt-hours. After reading the LCD display for the cumulative kWh, you can use this information to calculate the average amount of energy used by the appliance per day, week, month, or year.

Be sure to write down all the information or snap some pictures with your phone before unplugging the Kill A Watt Energy Meter because it doesn’t have a battery!

In my case, I left the refrigerator plugged into the Kill A Watt for 145 hours.  I also noted that the total energy used by the appliance in that time was 12.41 kWh.  

145 hours connected

Since I had the rate set at $0.25 per kWh, the Kill A Watt Energy Meter shows that, hypothetically, cost of running this refrigerator for 145 hours was $3.10… But I want more information than that!

Step 4. Do Some Math

With this information from the Kill A Watt, I’ll determine the monthly kWh used by the refrigerator. I’ll round the numbers off for simplicity.

12.41 kWh over 145 hours

To get the average amount of kWh used per hour, I divide the total kWh by the amount of time that’s passed since plugging it in.

12.41 kWh / 145 hours = 0.085 kWh used per hour
To get the average kWh used in a day, I multiply that hourly amount by 24 because there are 24 hours in a day.
0.085 kWh per hour x 24 hours in a day= 2.04 kWh per day
Now that I have the average amount of kWh used in a day, I can multiply that number by 30 to get the average monthly kWh (given that a month has about 30 days).
2.04 kWh per day x 30 days in a month= 61.2 kWh per month
I now have a rough estimate of the kWh used by the appliance in one month: 61.2 kWh. 
Remember how I set the cost at $0.25 per kWh?  Multiply that 0.25 by 61.2 kWh and you get $15.30.  
Now I know that it costs about fifteen bucks a month to keep this refrigerator running because it uses roughly sixty kilowatt-hours every month. 

I’ll probably be running around our office checking all our appliances now.  What should I test next?


Author: Tom Jackson

I believe clean, renewable energy is key to the evolution of society as a whole. Solar powers our planet, why not harness it to power humanity? Let's power our homes, our work, and our vehicles with solar energy. It begins with raising awareness and encouraging those around us to go green.

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1 Comment

  1. Well isn’t that a fun calculation. In my case, we have time of day billing, which is easy enough to calculate – just annoying. We have On-Peak, Mid-Peak, Off-Peak.

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