How do you compute for the power consumption if you say that it's consuming 20 watts is that per hour?

Question

if it's per hour does that mean i should multiply it based on a kilowatt hour price and the length of time i'm using it?

Answer 1

A device that is on constantly, that is rated 20 watts, uses 20 watt-hours every hour, or 480 watt-hours (0.48 kilowatt-hours) per day.  The electric bill is based on total kilowatt-hours used.  Some appliances, like a refrigerator or heater, are only using their rated power when they are running, and little or no power the rest of the time.

Answer 2

Watts are a measurement of an instantaneous rate, independent of time.

And to clarify for a kilowatt-hour is not a kilowatt-PER-hour but rather a kilowatt-TIMES-hour.

kilowatt-PER-hour would imply that you were removing an element of time from the measurement, when in fact you are adding one.

Answer 3

watts are already "per hour"

Watts are a unit of power, which is the rate of using energy. So watts are joules per second.

A more useful, but confusing unit of energy is the watt-hour, which you can get by multiplying number of watts by number of hours.

So, if your appliance is consuming 20 watts and you want to know how much energy that is in one day, then multiply by 24 to get 480 watt-hours. If electricity costs 10¢ per kW-hr, which is 10¢ per 1000 watt-hours, then the applicance costs you:

480 watt-hours x 10¢/1000 watt-hours = 4.8¢

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