Electricity is measured in two ways: using units of demand or capacity and using units of energy or usage.
Units of demand/capacity
Demand reflects the instantaneous amount of work required to perform the function desired (such as creating light or physical force, powering a microchip, etc.). Similarly, capacity reflects the instantaneous ability to provide the energy required to do work (such as generator capability to provide energy, transmission capability to transmit energy, etc.). Demand and capacity are commonly measured in the following units:
W = watt
kW = kilowatt
MW = megawatt
GW = gigawatt
To convert between these, you can use the following:
1 kW = 1,000 W
1 MW = 1,000 kW
1 GW = 1,000 MW
Units of energy/usage
Energy or usage reflects demand or capacity multiplied by the amount of time that demand or capacity is in use. For instance, a 15-watt light bulb used for 2 hours creates 15 watts X 2 hours = 30 watt-hours of usage. Energy and usage are commonly measured in the following units:
Wh = watt-hour
kWh = kilowatt-hour
MWh = megawatt-hour
GWh = gigawatt-hour
The conversions between the units are:
1 kWh = 1,000 Wh
1 MWh = 1,000 kWh
1 GWh = 1,000 MWh