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How To Calculate Your Electricity Bill

Updated: 04/15/2020

Whether you want to calculate your total electricity bill, see what’s eating up the most energy in your home or find out how much energy a specific appliance consumes, this guide has a method you can use.

Calculating Electricity Cost

If you just want to know how much electricity you are using in general, you can find the information easily by checking your most recent electricity bill.

The amount of electricity you used will be portrayed in kilowatt-hours (kWh). Electricity rates are charged by the kilowatt-hour. To determine your charge, your usage is multiplied by your electricity rate. 

How your electricity bill is calculated

However, your bill only tells you your total usage, not what that total usage is comprised of. If you want that information, you will have to follow one of the methods below.

Use Household Averages

If you want to take the easy way, you can just look at the energy averages for an average household in the US. These are those averages according to Energy Star:

  • Heating: 29%
  • Cooling: 17%
  • Water Heating: 14%
  • Lighting: 12%
  • Other: 11%
  • Electronics: 4%
Chart with breakdown of home energy use by percentage.

However, this does not reflect your specific usage. If you want to find average energy usage in your home each month, you have to follow one of these methods. 

  1. Purchase A Monitoring Device
  2. Manually Calculate Your Electricity Bill

What you choose will be based on how much time you want to put into it, and how much money you are willing to spend.

 1. Purchase a Monitoring Device

If you don’t mind spending some money and want accurate readings quickly, purchase an electricity monitoring device.

There are multiple devices for home energy monitoring out there, but the one with the best ratings (as of late 2019) is the Sense Energy Monitor. This device is installed directly into your electrical panel and records how much energy specific devices are consuming in real-time. 

The only downside to this method is that this device costs $300. There are similar monitors that are less expensive, but according to the reviews, these sensors are not as accurate and have a whole host of other issues.

You could also get an inexpensive $20 monitor to measure how much electricity a specific device or appliance uses. We recommend this method to make it easier for you to manually calculate your monthly electricity bill as well.

2. Manually Calculate Your Electricity Bill

This method will take more time, but it allows you to calculate your electricity bill without spending any money.

If you want to use this method with all or multiple electricity devices, make a list on a sheet of paper. This will help you keep track of the numbers that you need for the calculations. 

Divide that list into three sections: Electrical Appliance, Appliance Wattage, and Estimated Monthly Use (in hours).

Here’s an example:

A table to help you calculate your monthly energy bill

Starting Calculations

To calculate how much electricity each appliance or device uses, we will use two formulas. (Follow this link for a more in-depth explanation of the relationship between watts and kilowatt-hours.)

Table with formulas for calculation monthly electricity usage

We can get the information we need in three steps.

1. Determine the Wattage and Estimated Monthly Use Of The Electrical Appliance

The first thing that we need to do is find the wattage and estimated monthly use of every electrical appliance you want to measure. 

The wattage of the product is often labeled on the back of the product itself. If it should look like this:

If it is not labeled on the product, you can look at the original package or user manual to find the wattage. 

If you cannot find the wattage from the two methods above, you can find an average wattage for the product online. However, this will likely not be accurate, so we suggest you purchase a cheap energy monitor. 

A cheap energy monitor will run you about $20-$30 on Amazon and take care of the calculations for you. For instance, this electricity usage monitor will not only tell you the wattage of the product but it will also tell you how many kWh the electrical product uses.

If you do not want to perform any calculations, a simple energy monitor is the way to go.

Unless you are using a simple energy monitor, your estimated monthly electricity use of a device or appliance is just a best guess. If you don’t have one, write that best guess down. Ensure that your estimated monthly use is in hours or the calculations will not work.

After you determine your estimated monthly use and the product wattage of all the appliances you are measuring, you have everything you need to make your calculations.

2. Calculating Kilowatt-Hours (kWh)

We will be using the two formulas from above to find the amount of kWh a product consumes.

Table with formulas for calculation monthly electricity usage

First, we will find the watt-hours of a product. 

In our example, we will be using a 135-watt television, that has an estimated monthly use of 30 hours.

To find the watt-hours used, we will use the first formula: Watt-hours = Appliance Wattage * Estimated Monthly Use (in hours)

135 watts * 30 hours = 4,050 watt-hours

Table with formula for calculating watt-hours

Next, we must convert that into kilowatt-hours (kWh). This is because kWh is the unit of measurement for our electricity bills. 

To transfer watt-hours into kilowatt-hours, we use the second formula: Kilowatt-hours = Watt-hours/1,000
4050 watt-hours / 1,000 = 4.05 kilowatt-hours

Table with formula for calculating kilowatt-hours

Our 135-watt television used for 30 hours a month comes out to 4.05 kilowatt-hours a month.

Repeat these steps as needed to determine the power usage of all your devices and appliance products.

3. Calculating Total Kilowatt-Hours

The second step was the hardest part! You may even be done if you only wanted to track the kWh consumption of one or two products.

However, if you measured all of your electrical appliances, you have one last step. 

Find the sum of your kWh usage, by adding all of the product’s kWh usage together. 

This should give you a number that is relatively close to the kWh usage on your bill. And if you multiply your total kWh usage by your electricity rate (your electricity rate is also found on your bill), you should get a number close to the amount you paid on your electricity bill.

A quick note about heating and air conditioning. It can be hard to get an accurate measure of your estimated monthly usage of heating and A/C. If you have a smart thermostat, it can tell you how long it operates each month. If not, you can get an idea of the air conditioning’s/heating’s kWh usage by taking the sum of all other electrical appliances kWh usage, and then subtracting that sum from the total energy consumption listed on your bill. 

You’re Done!

You have everything you need to calculate how much electricity any of your electrical appliances and electronic devices are using. 

However, there is only so much electricity usage that you can cut. So if you want to save money on your electricity bill, find more information on switching electricity suppliers here on Switching electricity suppliers can help you save up to 30% on your electricity bill and you don’t even have to change your energy use!