Understanding Power Units: MW, GW & TW

A watt measures power – the rate at which electricity is being used or supplied. The prefixes mega, giga and tera simply change the scale: 1 megawatt (MW) is 1 million watts, 1 gigawatt (GW) is 1 billion watts or 1,000 MW, and 1 terawatt (TW) is 1 trillion watts or 1,000 GW.

The household comparisons in the graphic are approximate scale illustrations. Using EIA's reported average annual U.S. residential electricity purchases of 10,791 kWh per customer corresponds to an average load of about 1.23 kW. On that basis, 1 MW is roughly equivalent to the average demand of about 800 homes, 1 GW to about 800,000 homes, and 1 TW to about 800 million homes.

A key distinction is that MW, GW, and TW are units of power, while MWh, GWh, and TWh are units of energy over time. That distinction matters when comparing a facility's instantaneous or maximum electrical demand with how much electricity it consumes over a day, month, or year.