Wind Turbine Power Output Calculator
Estimate the electrical power a wind turbine produces from its rotor diameter, the wind speed, and its overall efficiency. Use it for early-stage siting decisions and to compare turbine models before going to full energy-yield software.
Last updated: May 2026
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About this calculator
This calculator applies the standard wind power equation, P = 0.5 · rho · A · v^3 · Cp, where rho is air density (1.225 kg/m^3 at sea level, 15 C), A is the swept rotor area (pi · r^2, with r = rotorDiameter / 2), v is the wind speed in m/s, and Cp is the power coefficient (efficiency / 100). The result is divided by 1,000 to convert watts to kilowatts. The cubic dependence on wind speed is the dominant term: doubling wind speed multiplies available power by eight, while doubling the rotor diameter multiplies it by only four. The efficiency input represents the overall conversion from kinetic wind energy to electricity at the turbine terminals, combining the aerodynamic Cp (theoretically capped at the Betz limit of 0.593), gearbox losses, and generator efficiency; modern utility-scale machines achieve roughly 0.35 to 0.45 in their sweet spot, while small turbines often sit between 0.20 and 0.30. Edge cases: the formula assumes a steady, uniform wind across the entire swept area and does not model cut-in speed (about 3 to 4 m/s), rated speed (about 12 to 14 m/s, where output plateaus), or cut-out speed (about 25 m/s, where the machine is shut down to protect itself). Above rated wind speed real turbines blade-pitch to hold constant power, so this equation will overestimate output in storms; below cut-in it overestimates because real turbines produce zero. Use steady, hub-height wind speed, not gusts or surface measurements.
How to use
Example 1: A utility-scale turbine with an 80 m rotor at 12 m/s wind and 35 percent overall efficiency. Compute area: pi * (80/2)^2 = 5,026.5 m^2. Apply the equation: 0.5 * 1.225 * 5,026.5 * 12^3 * 0.35 = 1,860,800 W, or roughly 1,861 kW. That is consistent with a typical 2 MW machine running near its rated point. Verify by halving wind speed to 6 m/s: power should drop by a factor of 8 to about 233 kW, which the calculator confirms. Example 2: A small backyard turbine, 5 m rotor at 8 m/s with 25 percent efficiency. Area is pi * 2.5^2 = 19.63 m^2, and power is 0.5 * 1.225 * 19.63 * 8^3 * 0.25 = 1,540 W, about 1.5 kW. Sanity check: a 5 m rotor in 8 m/s wind has roughly 6,160 W in the air; we extract 25 percent, giving 1,540 W. The cubic-in-wind-speed sensitivity means small siting improvements pay off enormously.
Frequently asked questions
Why does my calculated output differ from the turbine manufacturer's nameplate rating?
Nameplate (rated) power is the peak output a turbine produces only at or above its rated wind speed, typically 12 to 14 m/s, and is a marketing or specification figure, not an average. This calculator returns the instantaneous theoretical power at the wind speed you enter, multiplied by your efficiency figure. If you plug in a wind speed below the rated value, you will get less than nameplate, and if you exceed rated speed, this calculator will over-predict because real turbines blade-pitch to flatten the curve. To estimate annual energy production, you need to combine the wind speed distribution at the site (usually a Weibull distribution) with the turbine's power curve, not just one wind speed. Use the wind-turbine-annual-energy calculator for that step. Nameplate times hours per year over-states real output by a factor of 3 to 5.
What efficiency should I use if I do not know the turbine's coefficient of performance?
For modern three-bladed horizontal-axis utility turbines, an overall efficiency of 35 to 45 percent is a reasonable assumption; the aerodynamic Cp of these machines peaks near 0.45 to 0.50 and small gearbox, generator, and electrical losses pull the wire-to-wind efficiency down to roughly 0.35 to 0.45 across the operating range. Small residential turbines are considerably worse, with 0.20 to 0.30 typical, because they have higher relative friction losses and operate in turbulent, low-altitude wind. Vertical-axis turbines often run 0.15 to 0.30. Never use Cp values above 0.593, the Betz limit; values above that are physically impossible because some wind must keep flowing through the rotor for the disc to extract energy. When in doubt, 0.35 is a safe default for utility machines and 0.25 for small turbines.
Why is the cubic dependence on wind speed so important when choosing a site?
Because power scales as the cube of wind speed, a site with 20 percent more wind produces 73 percent more energy (1.2^3 = 1.728), and a site with 50 percent more wind produces 238 percent more energy. This is why utility-scale developers spend years on resource assessment campaigns with met masts and ground-based LiDAR; small differences in mean wind speed translate to huge differences in project economics. It also explains why turbines are built so tall: wind speed grows with height following a power law, and adding 20 m of hub height can lift annual production by 20 percent or more even though the rotor and generator are unchanged. For the same reason, picking a site on the lee side of a hill or behind a windbreak is catastrophic, and small turbines mounted on rooftops (where building wake dominates) almost always under-produce relative to projections.
When should I NOT use this calculator?
Do not use this single-wind-speed equation for project finance, grid planning, or any decision that requires the full annual energy figure; it ignores the wind speed distribution, the turbine's actual power curve (which is non-linear, has a cut-in and a cut-out, and flattens above rated speed), and array losses inside a wind farm (turbines downstream of others lose 5 to 15 percent to wake effects). Do not use it to size electrical equipment such as inverters, cables, or substation transformers; those are sized on rated power and on fault conditions, not on this average-case estimate. It is also unsuitable for very small turbines operating in heavily turbulent, low-elevation wind, where the steady-flow assumption breaks down badly. Treat this calculator as a back-of-the-envelope sanity check, not a design output. For real projects, use industry tools such as openWind, WAsP, or WindPRO together with at least one full year of on-site wind measurements.
What is the most common mistake people make with this calculation?
By far the most common mistake is plugging in surface-level wind speed (the figure you would read off a weather station 2 m above the ground or off a publicly available climate atlas) rather than hub-height wind speed. The turbine hub is typically 80 to 120 m up, where the wind is 30 to 50 percent faster than at ground level. Because power scales as the cube of wind speed, that height gap inflates the kinetic energy figure by a factor of 2 to 3, leading to wild over-prediction of output when you use the wrong reference. Other classic mistakes are confusing mean wind speed with the wind speed at which the turbine reaches rated power, ignoring air density correction for high-altitude or hot-climate sites (rho falls about 10 percent per 1,000 m of elevation), using gust speeds instead of sustained averages, and assuming efficiency higher than the Betz limit of 0.593. Each of these can introduce 20 to 50 percent errors on their own and they compound when combined. To avoid the height mistake, adjust ground-level wind to hub height using the wind-speed-height-adjustment calculator before entering it here.