A megawatt (MW) is a unit of power equal to one million watts, or 1,000 kilowatts. A gigawatt (GW) is 1,000 megawatts. Like the kilowatt, they measure how fast energy is produced or used at a given moment, so they are used to rate power stations, wind and solar farms, interconnectors and peak demand on the grid.
Power and energy
Power units describe a rate. Energy units add time: running at 1 MW for one hour produces or uses one megawatt-hour (MWh). The same rule as for the kilowatt-hour applies at every scale.
| Power | Energy over one hour | Equal to |
|---|---|---|
| 1 kW | 1 kWh | the unit on a household bill |
| 1 MW = 1,000 kW | 1 MWh | 1,000 kWh |
| 1 GW = 1,000 MW | 1 GWh | 1,000 MWh, or one million kWh |
| 1 TW = 1,000 GW | 1 TWh | 1,000 GWh, or one billion kWh |
Wholesale electricity is priced per MWh, while national output is usually counted in TWh per year.
A sense of scale
- Cleve Hill in Kent, the UK’s largest solar farm, is rated at 373 MW.
- The UK had 65.3 GW of renewable generating capacity at the end of 2025, including 16.6 GW of offshore wind.
- UK power stations generated about 294 TWh in 2025, of which 153.0 TWh, or 52.1%, came from renewables.
- Ofgem’s typical single-rate household uses 2,500 kWh of electricity a year, so 1 GWh would cover about 400 such homes for a year and 1 TWh about 400,000.
Capacity is not output
A rating in MW is a maximum. Wind and solar farms rarely run flat out, so their annual output is much lower than capacity multiplied by the 8,760 hours in a year. UK offshore wind had a load factor of 36.4% in 2025, which means each GW produced about 3.2 TWh over the year. Solar’s load factor was about 11%.
Read more: kW to kWh converter.