Calculate wind turbine rotor swept area from diameter, radius or blade length — and estimate the available wind power from wind speed, air density, Cp and electrical efficiency.
🌬️ Rotor Diameter → Swept Area → Available Wind Power
Rotor Diameter
Average Wind Speed
Air Density
Power Coefficient Cp
Electrical Efficiency
Rotor Type
VAWT Height Optional
For a normal horizontal-axis turbine, swept area is a circle. For simple vertical-axis turbines, use the rectangular approximation: area ≈ rotor height × rotor diameter.
Blade count does not change swept area. It is included only as a design note for comparing rotor types.
Blade length:0.5m1m1.5m2.5m5m
Target Electrical Power
Wind Speed
Air Density
Cp
Electrical Efficiency
Safety Oversize
This reverse mode estimates rotor size needed to reach a target output at the selected wind speed. Real turbines need a power curve and structural design checks.
Swept area depends on diameter squaredDoubling rotor diameter increases swept area by four times. This is why blade length has a very strong effect on turbine output.
Blade count does not change swept areaA 2-blade, 3-blade or 5-blade rotor with the same diameter sweeps the same circular area. Blade count affects speed, torque, noise and startup behavior.
Wind speed still matters moreWind power increases with wind speed cubed. Use the Wind Speed Height Calculator to estimate wind speed at a higher tower height.
Wind turbine swept area is the area covered by the rotor blades as they rotate. For a normal horizontal-axis wind turbine, the swept area is a circle. This circular area decides how much moving air passes through the rotor.
Why rotor diameter is so important
Rotor swept area increases with the square of diameter. A small increase in blade length can create a much larger collection area. That is why two turbines with similar generator ratings can behave very differently if their rotor diameters are different.
How to use this calculator
Use the diameter tab when you know the full rotor diameter. Use the blade length tab when you know the radius from hub center to blade tip. Use the target power tab when you want to estimate the rotor size needed for a selected electrical output at a given wind speed.
This calculator gives planning estimates. Real wind turbine design also needs blade aerodynamics, turbine power curve, cut-in speed, rated speed, cut-out speed, tower height, turbulence, generator loading, braking and structural safety checks.
❓ Frequently Asked Questions
For a horizontal-axis turbine, swept area is A = πr². If you know diameter, use A = πD²/4.
In practical calculation, blade length is usually treated as the rotor radius from hub center to blade tip. Actual blade geometry and hub size may slightly change the exact value.
No. Swept area increases with radius squared. If blade length doubles, swept area becomes four times larger.
At the same wind speed and efficiency, yes, more area means more available wind power. But actual output also depends on Cp, generator size, control system, turbine design and wind conditions.
Cp is the power coefficient. It represents how much of the wind power the rotor can capture. No turbine can capture 100% of the wind power.
Yes, use the vertical-axis option for a simple rectangular approximation. For many VAWT designs, swept area is estimated as rotor height multiplied by rotor diameter.
No. Swept area is only one part. Rated power also depends on wind speed, Cp, generator design, control strategy, rated speed and manufacturer limits.