One certainty in life is paying for the things you consume. We will always have bills, and one of these for owners and many renters is electricity.

But have you ever wondered how they know how much electricity you use?

One local utility, OhioEdison, explains it this way:

Electricity is measured and priced in kilowatt-hours (kWh). You are billed according to the number of kilowatt-hours you use as measured by your electric meter.

When you pay for a kWh of electricity, you are buying 1,000 watts of electricity used continuously for one hour. As an example, one kWh is the amount of electricity a 100-watt light bulb will use in ten hours.

But this is only a partial explanation. Even if you know what a kWh is, that’s not the same as understanding how they measure it so they can bill you for it.

Screenshot of an electricity measuring device from Harbor Freight

Measuring electricity flow

Sensitive devices can measure how much electricity is flowing through them without offering any impedance. That is, they don’t slow down the flow of electricity. They simply measure how much is rushing past.

This provides wattage measures. Many devices can actually measure more than that, but watts is the most important measure.

Then this is measured over time.

Watt = 1 unit of energy.

Kilowatt = 1000 units of energy

Kilowatt hours = number of kilowatts used over time

So if you have a lamp that draws 40 watts and you leave it on for 50 hours over the course of a billing cycle, you have consumed 2000 watts. Divided by 1000 to determine kw, you are then left with 2 kWh which is what will show up on your bill.

Of course, you have lots of different devices in your home, and each of them draws different amounts of electricity, for different lengths of time, over the billing period.

How much does each item draw? Well, you can find out.

You can measure this yourself

To get specific readings from individual outlets showing your energy use, you simply need one tool: a plug load monitor. This is an electricity usage monitor that reveals exactly how many kWh a device or appliance is drawing.

Plug this into an outlet then plug the device or strip into the monitor, and it will show you how much electricity those items draw.

Most monitors show you the high and low levels that the lamp or refrigerator or computer draws over time, and the average.

If you want, you can do a whole-house inventory to see where you are using most of your electricity.