How to Calculate KWH on 240v Appliances

Look for the appliance manufacturer’s nameplate on the appliance. This nameplate, typically found on the front or back of a 240-V appliance, will contain the model and serial numbers as well as information on the electric demand of the appliance when it is operating. Look at whether the demand is expressed in watts or amps. If it is given in watts, skip Step 2 and go to Step 3.

Multiply the volts times the amps to get watts. For instance, if the manufacturer of your 240-V electric clothes dryer says it draws 10 amps when operating, multiply 240 V times 10 amps to get 2,400 watts of power demanded by your dryer when it is on.

Convert watts to kilowatt-hours. One kilowatt-hour is equal to 1,000 watts of power demand on line for one hour. To find kilowatt-hours, or KWH, multiply the watts times the number of hours per day the appliance operates, divide that product by 1,000 to get daily kilowatt-hour consumption. For example, a dryer that draws 2,400 watts and is used for three hours a day will consume 7.2 kilowatt-hours per day. Multiply the daily consumption figure by 30.5 days to get average monthly consumption. In this example, the dryer will consume an average 219.6 kilowatt-hours per month.