Locate the manufacturer's tag or sticker typically located at the side or bottom of your appliance. Each appliance has a tag that contains information about its voltage, wattage and ampere rating.
Copy the wattage on a piece of paper. In case there is no wattage indicated, multiply the voltage by the ampere rating to get the equivalent watts (example: 110 volts x 10 amperes = 1,100 watts).
Multiply the number of watts by the number of hours the appliance is used (example: 1100 watts x 10 hours = 11,000 watt hours). Divide the watt hours by 1,000 to get the number of kilowatt-hours used (example: 11,000 watt hours / 1,000 = 11 KWh).