How to Calculate Watts to KWH
Watts and kilowatthours, or kWh, are units of power commonly employed to measure electrical power usage. Watts are usually encountered with light bulbs; for instance a 100 watt bulb. A kWh, on the other hand, is a unit that also includes time, and corresponds to 1,000 watts used for a full hour (think of ten such light bulbs burning together for one hour.) The kWh is the unit used to figure your electric company bill. By adding up the watts used and the amount of time they are used for, you can calculate kilowatt hours, and even make an estimate of your household efficiency or what your electric bills will be.

Find the wattage of the electrical items you are measuring. If the wattage is not printed on the unit, check the manual to see what the wattage is.

Figure out, measure or estimate the number of hours each unit will run for the time period you are measuring.

Multiply the wattage by the number of hours used to get a figure for watthours for each unit. As an example, if you have an appliance that runs at 200 watts, and you use it for 4 hours, that is 800 watthours.

Add the total of watthours for all the units you are measuring.

Divide the watthours total by 1,000 to get a figure for kWh. If your watthour total is 15,000, for instance, your kWh total is 15.
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