Kilowatt-hour is the commercial unit of electric energy.
The basic unit of energy is the joule or watt-second. An electrical energy is said to be one joule when one ampere of current flows through the circuit for a second when the potential difference of one volt is applied across it.
Commercial unit of electrical energy
The commercial unit of electrical energy is the kilowatt-hour (kWh) which is also known as the Board of Trade unit (B.O.T).
1 kwh = 1000 × 60 × 60 watt-second
1 kwh = 36 × 105 Ws or Joules
Generally, one kwh is called one unit.