The commercial unit of energy is the kilowatt-hour (kWh). The quantity of energy utilised by a device in one working hour at a constant rate of one kilowatt is defined as one kilowatt-hour.

The Joule is the Si unit is of energy.

As a result, 1 kWh = 1kW x 1h = 1000W x 1h = 1000(J/s) x 3600 s = 3.6 x106 J is the link between commercial and Si unit iss of energy.