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How to Calculate Kilowatts — Measuring Electricity Usage

Posted on by Everything Energy 5 minutes, 18 seconds

Watts up? We’re diving into the science of watts (W) and how to calculate kilowatts (kW) so you can better understand your energy consumption and the energy costs associated with running electronics and appliances in your home.

Let’s start from the beginning.

What is a watt?

A watt is a unit of power in the International System of Units (SI) equal to one joule of work performed per second (or 1/746 horsepower.) Basically, it’s the rate at which energy is consumed. The symbol for a watt is “W.”

The term “watt” is named after famed Scotsman James Watt. His contributions as an inventor, engineer and instrument maker — including his improvements to steam engine technology — helped usher in the Industrial Revolution.

One watt is pretty small in the grand scheme of things. Some electronics — like smartphones — only need a few watts to operate. Others, like kitchen appliances or generators, can take 1,000 or more watts to operate. In these instances, it’s helpful to talk in terms of kilowatts.

What are kilowatts, megawatts and gigawatts?

One kilowatt is equal to 1,000 watts. The symbol for a kilowatt is kW. To calculate kilowatts from watts, you would use this equation:

kW = W ÷ 1,000

If you’re talking about much larger amounts of power, you may want to use the term megawatts. A megawatt is equal to 1 million watts. The symbol for a megawatt is MW. To calculate megawatts from watts, use this equation:

MW = W ÷ 1,000,000

On an even larger scale, you can talk about power in terms of gigawatts. A gigawatt is equal to 1 billion watts. The symbol for a gigawatt is GW. To calculate gigawatts from watts, use this equation:

GW = W ÷ 1,000,000,000 To put it in perspective, 1GW of power is equivalent to about 100 million LED bulbs or 310 utility-scale wind turbines. As consumers, we don’t often talk about personal energy consumption in terms of gigawatts or even megawatts. We usually use the terms kilowatts and kilowatt-hours (kWh).

What is the difference between kilowatts vs. kilowatt-hours?

A kilowatt and a kilowatt-hour are both units of energy. However, a kilowatt-hour is equal to the energy expended by one kilowatt (1,000 watts) in one hour. 

On your utility bill, you’ll see your electricity usage listed in kWh. It’s helpful to know how much energy an electricity-consuming item uses in an hour and how much you spend running each of your electronic devices and appliances. To do this requires a little bit of math.

How to calculate kilowatt-hours of an appliance

To calculate the energy consumption of any electronic device or appliance, you first need to know its wattage. This can usually be found on the device itself or an attached label.

Then, you’ll want to figure out how many hours a day you use that item.

Once you have that information, multiply the wattage by the amount of time the item is used. The result will give you the number of watt-hours (Wh) the item uses. The equation looks like this:

Wh = W x hours of usage

For example, if you have a 65W lightbulb that is turned on for 3 hours a day, you could use this equation:

65W x 3 hours = 195Wh

But these calculations provide energy usage as watt-hours. Since utilities measure our electricity usage in kilowatt-hours, we need to divide the watt-hours by 1,000. In our previous lightbulb example, that would look like this:

195Wh ÷ 1000 = 0.195kWh

One 65W lightbulb used for 3 hours per day would consume 0.195kWh of electricity.

Now that you know how to calculate kilowatts and kilowatt-hours, you can now figure out how much using this lightbulb — or any electronic item — will cost.

How to calculate kWh cost and cost to operate electronics

To find how much a kWh costs, you need to look at your electric bill. You should look for the average price you pay per kWh, which if on a bundled plan should include any other applicable fees like base charges and TDSP delivery charges. Knowing this information, you can calculate how much it costs to operate electronics in your home.

To do this, you would simply calculate how many kWh your electronic item uses in a day and multiply that by your cost per kWh:

Cost of operation = kWh used x cost per kWh

If your cost per kWh is $0.15, you can figure out how much it costs per day to use that lightbulb in our example:

0.195kWh x $0.15 = $0.029

To use that 65W lightbulb for 3 hours a day, it costs you about 3 cents. While this is a small amount, remember: that’s only the cost to run one lightbulb for one day. Larger and/or more frequently used electronics and appliances can cost more to operate.

Take, for example, a 5,000W clothes dryer. If you run it for one load that takes one hour, that would use 5kWh. Using $0.15/kWh, that load costs about $0.75. Three loads a week equals $2.25, and about $9 per month. You can see how quickly using electricity around your home adds up!

How to calculate kilowatts using a watt meter

You may now be wondering about all the various electronics in your home. How much does my old refrigerator consume? How much energy is lost to phantom load when I leave charged items plugged in? Is leaving my laptop on 24/7 adding significant cost to my electric bill?

To answer these questions, you may want to purchase or borrow a tool called a watt meter. To use a watt meter, plug it into the wall and then plug an electronic device into it. You can see over a period of hours how many kWh are consumed. And when you input your cost per kWh into the watt meter, it will calculate how much that item costs to operate.


As you’ve just learned, a little bit of math can help you better understand how you use energy at home. It can also empower you to take charge of your electricity usage and your electric bill.

Another way to take charge when it comes to energy is to find the best electricity plan for your home, family and needs. Everything Energy provides the tools you need to shop for electricity, see bill estimates based on your usage history and make apples-to-apples comparisons. Try it out now for free! 

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