The kilowatt-hour (symbolized kW⋅h) is a unit of energy equivalent to one kilowatt (1 kW) of power sustained for one hour. One watt is equal to 1 J/s. One kilowatt-hour is 3.6 megajoules, which is the amount of energy converted if work is done at an average rate of one thousand watts for one hour. Note that the international standard SI unit of energy is the joule. The hour is a unit of time outside the SI, so the kilowatt-hour is a non-SI unit of energy.