The power generated by a power station is measured in multiples of the watt, typically megawatts (10 watts) or gigawatts (10 watts). Power stations vary greatly in capacity depending on the type of power plant and on historical, geographical and economic factors. The following examples offer a sense of the scale.
Many of the largest operational onshore wind farms are located in China. As of 2022, the Roscoe Wind Farm is the largest onshore wind farm in the world, producing 8000 MW of power, followed by the Zhang Jiakou (3000 MW). As of January 2022, the Hornsea Wind Farm in United Kingdom is the largest offshore wind farm in the world at 1218 MW, followed by Walney Wind Farm in United Kingdom at 1026 MW.
In 2021, the worldwide installed capacity of power plants increased by 347 GW. Solar and wind power plant capacities rose by 80% in one year. , the largest photovoltaic (PV) power plants in the world are led by Bhadla Solar Park in India, rated at 2245 MW.
Solar thermal power stations in the U.S. have the following output:
:Ivanpah Solar Power Facility is the largest of the country with an output of 392 MW
Large coal-fired, nuclear, and hydroelectric power stations can generate hundreds of megawatts to multiple gigawatts. Some examples:
:The Koeberg Nuclear Power Station in South Africa has a rated capacity of 1860 megawatts. 
:The coal-fired Ratcliffe-on-Soar Power Station in the UK has a rated capacity of 2 gigawatts.
:The Aswan Dam hydro-electric plant in Egypt has a capacity of 2.1 gigawatts.
:The Three Gorges Dam hydro-electric plant in China has a capacity of 22.5 gigawatts.
Gas turbine power plants can generate tens to hundreds of megawatts. Some examples:
:The Indian Queens simple-cycle, or open cycle gas turbine (OCGT), peaking power station in Cornwall UK, with a single gas turbine is rated 140 megawatts.
:The Medway Power Station, a combined-cycle gas turbine (CCGT) power station in Kent, UK, with two gas turbines and one steam turbine, is rated 700 megawatts.
The rated capacity of a power station is nearly the maximum electrical power that the power station can produce.
Some power plants are run at almost exactly their rated capacity all the time, as a non-load-following base load power plant, except at times of scheduled or unscheduled maintenance.
However, many power plants usually produce much less power than their rated capacity.
In some cases a power plant produces much less power than its rated capacity because it uses an intermittent energy source.
Operators try to pull maximum available power from such power plants, because their marginal cost is practically zero, but the available power varies widely—in particular, it may be zero during heavy storms at night.
In some cases operators deliberately produce less power for economic reasons.
The cost of fuel to run a load following power plant may be relatively high, and the cost of fuel to run a peaking power plant is even higher—they have relatively high marginal costs.
Operators keep power plants turned off ("operational reserve") or running at minimum fuel consumption ("spinning reserve") most of the time.
Operators feed more fuel into load following power plants only when the demand rises above what lower-cost plants (i.e., intermittent and base load plants) can produce, and then feed more fuel into peaking power plants only when the demand rises faster than the load following power plants can follow.