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Why Do We Measure Electricity in Kilowatt-Hours (kWh)?

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If you’ve ever taken a good look at your electricity bill, you’ve probably noticed that your service provider measures your energy in kilowatt-hours (kWh). In fact, nearly every household appliance, device, and gadget uses this unit of measurement. But what exactly are kWhs, and why do we use them so often?

In this article, we explore everything there is to know about kilowatt-hours, how we calculate them, and why we need to measure electricity in the first place.

kilowatt hours measured on electrical meter

Why Do We Measure Electricity in the First Place?

If you give this question any thought, you’ll probably find the answer is quite obvious. We need a standard unit of measurement to understand how much one device’s consumption compares to another. We also need a way to measure how much energy we produce.

For example, common sense tells us that a light bulb will consume far less energy than an air conditioner, but exactly how much? And how do we know we’ll have enough power to run both at the same time? This is why it’s essential to have a consistent way of measuring electricity. 

What Does a Kilowatt-Hour Measure?

In order to understand this, we must first understand watts. A watt tells you how much energy is being used by a device. In fact, you can find out how many watts a device is using by multiplying the volts by the amps. Therefore, it tells you the rate of power flowing to your device. 

a line of lightbulbs lit up with a black background

A kilowatt, on the other hand, is one watt times 1,000. Much like kilograms and kilometers, a kilowatt is simply a better fitting unit for larger measurements. 

So, now that we understand watts and kilowatts, what does a kilowatt-hour measure? Essentially, it tells us the total amount of energy used over time. For instance, one kWh equals 1ooo watts of power consumed over the course of an hour. Thus, different devices will consume different amounts of energy over time. For example, a light bulb might take 10 hours to consume one kWh, while a microwave may consume one kWh in less than 15 minutes.

It’s also possible to use KWh to calculate how much energy has been generated. For example, a solar panel system producing 1000watts for one hour will generate 1Kwh of energy.

solar charge controller yield
This is an example of a solar charge controller output measurement showing how much energy it produced in kWh

Kilowatt Versus Kilowatt-Hour: What’s the Difference?

So what is the real difference between kilowatts and kilowatt-hours? The answer comes down to instantaneous power versus energy used over time. A kilowatt is just the name for 1,000 watts. These 1,000 watts could be consumed all at once, or they could be consumed over four hours. We really don’t know because all we learn from this is the amount of energy, not the time. 

Kilowatt-hours tell us the number of kilowatts and how long it takes to consume them. Getting back to our microwave versus light bulb example, both will consume one kilowatt, but how long does it take for each of them to do so? That’s what kilowatt-hours tells us: the actual flow of energy in usable terms. 

In descriptive terms, we call watts or kilowatts “power” and kWh “energy”.

microwave timer being adjusted by a hand

Why Is Electricity Measured in Kilowatt-Hours?

It’s actually not measured just in Kilowatt-Hours, but any derivative of the watt. This could be watt-hours (Wh) or even megawatt-hours (Mwh).

Electricity is measured in kWh simply because it’s so easy to convert across all spectrums of electricity usage. You can use watt-hours if you need to measure energy on a small scale, or you can use megawatt (one kilowatt x 1,000) hours if you’re calculating large amounts of energy usage. 

Moreover, the greater electrical grid uses this measurement to calculate how much energy each household uses, thus, electricity consumption is measured this way on everything from your appliances to your power bill. Why? Because it’s simply the best way to standardize the amount of energy we all use. 

How Do You Calculate a Kilowatt-Hour?

As mentioned before, one kilowatt consumed over the course of an hour equals one kWh. Therefore, you would use one kWh if you kept a one-kilowatt device running for one hour. If you kept it running for two hours, you would use two kWh, and so on and so forth. You need to know watts and time to figure out Kwh.

Here are a few examples.

1000w x 1Hr = 1kWh

1W x 1000Hr = 1kWh

1W x 1Hr = 1Whr or since 1kWh = 1/1000kWh .001Kwh

20w x 3Hr = 60Wh/1000kWh = .06kWh

400w x 24Hr = 9600Wh/1000kWh = 9.6kWh

Powerlines with a sunset in the background

kWh are used to determine household energy use, but the power grid measures in millions of watt-hours or Megawatt-Hours.

Kilowatt-Hour Versus Amp-Hour: What’s the Difference?

Remember the equation to determine watts? Volts x amps = watts.

In this case, volts are like the water pressure flowing through a pipe, while amps signify the volume. This then determines the flow (i.e., the watts). And how do we determine the flow of energy over time? You guessed it: kilowatt-hours. 

But without the volts, you just have amps. Therefore, an amp-hour is really just the current of charge over an hour. We need volts to measure the energy, so amp-hours is the measure of charge and is usually reserved for a battery size measurement.

→ Still confused? Don’t worry. We’ve broken it down in this article: How to Calculate and Compare Watt Hours to Amp Hours

Know Your Energy Usage

Measuring electricity is vital when it comes to ensuring our appliances are working properly. This is where kilowatt-hours come in handy. They’re a convenient way to determine how much energy we’re consuming over time, and we use them in a wide variety of circumstances.

After all, each of our appliances uses a certain amount of kilowatts when running. Without this measurement, we wouldn’t know how much power we need to run those electronics in the first place. When planning an off-grid solar or backup power system, it’s necessary to know how much energy you’re using to properly size your battery bank and system components.

Do you have any questions about kilowatt-hours or electricity in general? Drop them in the comments below!

woman understanding energy usage kwhs by watching a video on her phone

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