The kilowatt hour is commonly used for electrical energy, since it may be easier to understand in a practical context than the proper SI unit for energy, the joule, which is a watt second (W?s). The joule is a comparatively small unit, making numbers quite large.
1 kW?h = 3,600,000 joules.
The kilowatt hour is a commonly used unit of billing for electric utility companies, although many companies are moving to use the unit megajoule(MJ) instead.\n