How do you convert watts to KWh?

To convert between watts to kilowatt-hours, first convert to kilowatts by dividing by 1,000, then multiply by the number of hours that the device is in use. For example, a 60-watt bulb that is on for five hours uses 0.06 kW per hour, for a total of 0.3 kWh.

A 60W incandescent bulb left on for five hours a day, over the course of a month, uses 9 kWh of energy. In the United States, as of 2015, residential power costs an average 12.6 cents per kWh, so this single incandescent bulb adds roughly $1.13 to a home owner's monthly electrical bill.