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Wind Turbine Specific Power (Rated Power per Square Metre of Rotor)

Also known as specific power of a wind turbine · rated power per swept area · watts per square metre of rotor · W/m2 of a wind turbine rotor · specific rating of a turbine · low specific power turbine · turbine rating over rotor area · generator size against rotor size · rated capacity over swept area

SP=PratedA=4 Pratedπ D2\mathrm{SP} = \frac{P_{rated}}{A} = \frac{4\,P_{rated}}{\pi\,D^{2}}
sig figs

Worked example: USWTDB GE1.5-77: 1 500 kW, 77 m rotor → 322.12 W/m². Press Try an example to run it live, then adjust anything.

Enter your known values, leave one input blank, and solves for the missing one. Tap a variable’s symbol to see what it means, with a typical value. Change any unit and the answer follows.

Where Wind Turbine Specific Power (Rated Power per Square Metre of Rotor) fits

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See also

Wind Turbine Power Output: Solve it for the wind speed with the rated power and the swept area to get the rated wind speed for your own air density and power coefficient.Rotor Swept Area: The area in the denominator, from the rotor diameter.Wind Power Density: The power in each square metre of the wind itself, to compare with the specific power the generator is sized for.Capacity Factor: What a lower specific power tends to raise: the share of the year a turbine runs near its rating.Photovoltaic Array Power Density (Capacity per Square Metre of Array): The same watts-per-square-metre idea for a solar array.
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Wind Turbine Specific Power (Rated Power per Square Metre of Rotor) explained

DAPratedSPper rotor area

Specific power says how much generator a wind turbine has for the air its rotor sweeps: the rated power divided by the swept area. The swept area is the circle the blade tips sweep, A=πD2/4A = \pi D^{2}/4, so the formula needs only the rated power and the rotor diameter. The rated power is the nameplate figure, the stated output power at the rated wind speed, and the answer is in watts per square metre. A lower number means a larger rotor on the same generator.

Reading the answer. A turbine with a low specific power reaches its rated power in lighter winds and, in a given wind, runs closer to its rating more of the time, so a low value suits a lighter-wind site. The link to the wind is the turbine power equation: the specific power is half the air density times the power coefficient times the rated wind speed cubed. With air at 1.225 kg/m³ and a power coefficient of 0.45 at rated speed, 322 W/m² means a rated wind speed near 10.5 m/s. The wind turbine power page solves that equation for the speed with your own density and coefficient.

Worked examples from the database. A GE 1.5-77 is rated at 1 500 kW with a 77 m rotor (swept area 4 656.63 m²), and 4×1.5×106/(π×772)4 \times 1.5\times10^{6} / (\pi \times 77^{2}) gives 322.12 W/m². A GE 2.8-127 at 2 800 kW with a 127 m rotor has 221.03 W/m², a Vestas V150-4.2 at 4 200 kW with 150 m has 237.67, and a Vestas V90-3.0 at 3 000 kW with 90 m has 471.57, the most generator for its rotor of these. Backward, 322.1216592 W/m² over a 77 m rotor is 1 500 kW, and 2 800 kW at 221.0348 W/m² needs a rotor of 127 m.

Source and limits. The inputs come from the United States Geological Survey's United States Wind Turbine Database (version 9.1, September 2026), which lists the rated capacity, the rotor diameter and the swept area of every turbine in the country. Specific power says how a machine is sized, not how much energy it delivers: the share of the year a turbine runs near its rating is its capacity factor, which a lower specific power tends to raise.

Wind Turbine Specific Power (Rated Power per Square Metre of Rotor) formula

SP=PratedA=4 Pratedπ D2\mathrm{SP} = \frac{P_{rated}}{A} = \frac{4\,P_{rated}}{\pi\,D^{2}}
Where
  • SP\mathrm{SP}= Specific power (W/m²)
  • PratedP_{rated}= Rated power (kW)
  • DD= Rotor diameter (m)
Where this comes from
  • U.S. Geological Survey, United States Wind Turbine Database (USWTDB), ver. 9.1, September 2026 (Hoen and others; US federal work, public domain): t_cap is the 'turbine rated capacity, stated output power at rated wind speed' in kilowatts, t_rd the rotor diameter in metres and t_rsa the rotor swept area in square metres. Read through the open API on 23 Oct 2026: GE1.5-77 1 500 kW, 77 m, 4 656.63 m2; GE2.8-127 2 800 kW, 127 m, 12 667.69 m2; Vestas V90-3.0 3 000 kW, 90 m, 6 361.73 m2; Vestas V150-4.2 4 200 kW, 150 m, 17 671.46 m2. The DataCite record of the DOI was checked the same day. Read it
Revised 30 October 2026
Cite this page

formula.expert. (2026, October 30). Wind Turbine Specific Power (Rated Power per Square Metre of Rotor) Calculator. https://formula.expert/solvers/wind-turbine-specific-power

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