What is a good wind power density for a wind farm?

Generally, sites with WPD above 400 W/m² (NREL Class 4) are considered commercially viable for utility-scale wind. Class 5 (500–600 W/m²) and above are excellent. Class 3 (300–400 W/m²) may work for community or small commercial projects.

Why does wind speed have a cubic effect on power?

Kinetic energy is proportional to v², and power is energy per unit time, so when more air arrives per second (proportional to v), the total power scales as v × v² = v³. Doubling wind speed increases power density eightfold.

What air density should I use?

Sea level at 15 °C is 1.225 kg/m³ (standard atmosphere). Air density decreases roughly 1.1 % per 100 m of elevation and also decreases with temperature. For quick estimates use 1.225; for a real site use 1.2929 × 273.15 / (273.15 + T_celsius) × P_Pa / 101325.

How does this relate to actual turbine output?

WPD is the theoretical limit. A real turbine captures only a fraction: multiply WPD × Rotor Area × Cp (power coefficient, typically 0.35–0.45) × drivetrain efficiency. The Betz limit sets an absolute ceiling at Cp = 0.593.

What are the IEC wind speed classes?

IEC 61400-1 defines turbine design classes by reference wind speed (50 m/s for Class I, 42.5 m/s for Class II, 37.5 m/s for Class III). NREL's wind resource classes (1–7) are based on WPD at 50 m hub height and are more commonly used for site suitability ratings.

Wind Power Density Calculator

Name: Wind Power Density Calculator
Availability: InStock
Author: Nham Vu

Calculate wind power density (W/m²) from wind speed and air density to classify wind resource potential.

Site Parameters

Wind Speed

Air Density (kg/m³)

Standard sea-level air at 15 °C = 1.225 kg/m³

Estimate air density from altitude & temperature

Altitude (m above sea level)

Temperature (°C)

Rotor Diameter (m) (optional)

Wind Power Density

Enter parameters and click Calculate.

NREL Wind Resource Classes (50 m hub height)

Class	WPD (W/m²)	Description
1	< 200	Poor — generally not viable
2	200–300	Marginal
3	300–400	Fair — small/community wind
4	400–500	Good — utility-scale viable
5	500–600	Excellent
6	600–800	Outstanding
7	> 800	Superb — offshore / mountain ridge

Summary

Calculate wind power density (W/m²) from wind speed and air density to classify wind resource potential.

How it works

Enter the mean wind speed at hub height in meters per second (m/s) or miles per hour.
Enter the air density at the site — standard sea-level air is 1.225 kg/m³, but elevation and temperature reduce it.
The calculator applies the wind power density formula: WPD = 0.5 × ρ × v³.
The result is displayed in W/m² alongside the IEC/NREL wind resource class (Class 1–7).
Use the class rating to compare candidate sites and decide whether installation is economically viable.

Use cases

Pre-feasibility screening of onshore and offshore wind farm sites.
Comparing multiple candidate locations using the same air-density-adjusted metric.
Translating anemometer readings into energy-density figures for reports.
Teaching students and engineers the cubic relationship between wind speed and power.
Adjusting for high-altitude or tropical sites where air density differs from 1.225 kg/m³.
Estimating power available before applying turbine efficiency (Betz limit, rotor Cp).

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu