Residential electricity: what is a kiloWatt*hour (kWh)?

The tutor takes a detour from his solar energy series to explain kiloWatt*hour.

A kiloWatt*hour means 1 kiloWatt multiplied by 1 hour. (The asterisk means “times.”)

A Watt is energy used per second – aka, power. The unit is named for James Watt, developer of the steam engine.

To calculate the energy used, you must multiply the rate (aka, the power) by the time:

Energy used = power x time = Watts*seconds

The electric company doesn’t charge for power, but rather for energy. A simple conception is that each second, they multiply the rate you are using it (in Watts) by one second. They do this every second, then add up all those values to get your monthly (electrical) energy usage.

If you average out the rate of electrical use for a typical household, you might find it’s around 1275W. At the same time, there are 60*60*24*30=2592000s in a month. Therefore, the energy used might be


To make the numbers easier to process, the company divides the power by 1000, changing the Watts to kiloWatts (in Metric, kilo means 1000):


Next, they divide the seconds by 3600, converting the time to hours:


That’s the meaning of kWh and why the unit is used:)


BC Hydro

Giancoli, Douglas C. Physics, fifth ed. New Jersey: Prentice Hall, 1998.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

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