Power is a measure of the amount of work an electric current can accomplish in a specified period of time. The most common unit of electrical power measurement is the watt, or kilowatt, which is 1,000 watts. Power is the rate at which electrical energy is converted into some other form of energy such as light, heat or mechanical work or horsepower.

For any electrical device, the higher its power rating in watts, the greater its consumption of electrical energy, not necessarily the amount of work it produces. For example, consider a 100-watt incandescent light bulb. The 100 watts does not represent how much light it produces, but how much electrical power it uses. A 17-watt fluorescent lamp may produce much or even more light, while using only 17% of the power.

Appliance manufacturers normally indicate how much electrical power an appliance uses in units of watts.

Electric utilities measure the power consumption of their customers in kilowatts, thousands of watts, and measure the power produced by a generator or power plant in units of megawatts, or millions of watts.

U.S. motor manufacturers still rate motors in units of horsepower where one horsepower equals 746 watts.

The symbol for "power" is a capital "P". The kilowatt is shown as "kW" with a little k and capital W. The megawatt is shown as "mW" with a little m and capital W.