The Kilowatt-hour (kWh) is a unit of energy,which is equivalent to one kilowatt (1 kW) of power,
expended for one hour (1 h) of time.
Any energy expenditure of 1 kWh represents 3,600,000 joules

(3.600 x 10^{6})
To obtain joules one must multiply kilowatt-hour by 3.600 x 10^{6}.

And to obtain kilowatt-hour when joules are known, then multiply by 2.778 x 10^{-7}
In general, energy (E) is equivalent to power (P) multiplied by time (t).
To determine E in kilowatt-hours, P must be expressed in kilowatts and t must be
expressed in hours.

Suppose,

a 2.5 kW electric fan runs for 4 hours.

Then, P = 2.5 and t = 4, so the Energy E in kilowwatt-hours is:

**E = P x t = 2.5 x 4 = 10 kWh **

The consumption of electrical energy by homes and small businesses is usually
measured in kilowatt-hours. Larger businesses and institutions sometimes use the
megawatt-hour (MWh), where

1 MWh = 1,000 kWh. The energy outputs of large power
plants over long periods of time, or the energy consumption of states or nations,
can be expressed in

gigawatt hours (GWh),
where 1 GWh = 1,000 MWh = 10

^{6} kWh.