Part 1: Electrical Energy and Power Power is how strong an appliance is at the moment. It is measured in Watts. Energy is the total amount of electricity used over a certain period of time. It is measured in Kilowatt-hours. Calculate the cost: First, you take the Watts of the appliance and divide by a thousand to get Kilowatts. Then you multiply by the number of hours to get Kilowatt-hours. Finally, you multiply by the price of electricity. Energy efficient: A device is energy efficient if it us