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Wind Power Density Calculator

Reviewed by the CalculatorHub team, edited by James Graham. Standard kinetic energy of wind formula per NREL and DOE wind resource assessment methodology. Last verified 14 June 2026.

Wind power density (WPD) quantifies the wind energy resource at a site. It is the fundamental input for wind turbine selection and energy yield estimation. The formula WPD = 0.5 x rho x V^3 comes directly from the kinetic energy of moving air and is used by NREL, DOE and wind developers worldwide. Enter wind speed in metres per second and air density (which you can estimate from altitude) to get WPD in W/m2 and the NREL resource class. The calculator also shows the extractable power applying the Betz limit.

Mean wind speed at hub height; typical utility wind sites average 6 to 10 m/s
Elevation above sea level in metres. Used to compute air density per ICAO standard atmosphere.
1.23 kg/m3
209.83 W/m2
124.53 W/m2
Class 2 (Marginal)

Wind power density formula

WPD = 0.5 × rho × V3 [W/m2]
rho = 1.225 × (1 - 0.0000226 × h)4.256 [kg/m3]
Betz power = WPD × 16/27

Where V is wind speed in m/s, rho is air density in kg/m3 computed per the ICAO International Standard Atmosphere, and h is altitude in metres. The Betz limit (16/27 = 0.5926) is the theoretical maximum extractable fraction of wind power. Source: NREL Wind Resource Assessment Handbook; ICAO Doc 7488 Standard Atmosphere.

NREL wind power density resource classes (at 50 m hub height)

  • Class 1 (below 200 W/m2): Poor. Not suitable for utility-scale development.
  • Class 2 (200 to 300 W/m2): Marginal. May be viable with small turbines or community projects.
  • Class 3 (300 to 400 W/m2): Fair. Minimum threshold for utility-scale wind farms.
  • Class 4 (400 to 500 W/m2): Good. Commercially viable in most markets.
  • Class 5 (500 to 600 W/m2): Excellent. High-yield commercial development.
  • Class 6 (600 to 800 W/m2): Outstanding. Premium wind resource.
  • Class 7 (over 800 W/m2): Superb. World-class wind resource.

Wind power density: frequently asked questions

What is wind power density (WPD)?

Wind power density (WPD) is the amount of power available per unit area of a wind turbine rotor, expressed in watts per square metre (W/m2). It is calculated as WPD = 0.5 x rho x V^3, where rho is air density (kg/m3) and V is wind speed (m/s). Wind power varies with the cube of wind speed, meaning that doubling wind speed increases wind power 8-fold. WPD is the standard metric used by NREL and DOE for wind resource assessment.

What are the NREL wind power density classes?

NREL Wind Resource Classification (from the AWS Truepower wind resource atlas): Class 1 (below 200 W/m2 at 50 m) is poor; Class 2 (200 to 300 W/m2) is marginal; Class 3 (300 to 400 W/m2) is fair and suitable for most commercial turbines; Class 4 (400 to 500 W/m2) is good; Class 5 (500 to 600 W/m2) is excellent; Class 6 (600 to 800 W/m2) is outstanding; Class 7 (over 800 W/m2) is superb. These classes are defined at 10 m and 50 m hub heights.

Why does wind power increase with the cube of wind speed?

Wind power is kinetic energy per unit time passing through a rotor disk. Kinetic energy = 0.5 x m x V^2. The mass flow rate through the rotor is m = rho x A x V (density x area x velocity). Therefore Power = 0.5 x rho x A x V x V^2 = 0.5 x rho x A x V^3. This cubic relationship is why siting turbines in high-wind locations is so critical: a 50% increase in average wind speed more than triples available power.

How does altitude affect air density and wind power?

Air density decreases with altitude following the ICAO Standard Atmosphere: rho = 1.225 x (1 - 0.0000226 x h)^4.256 kg/m3, where h is altitude in metres. At 1,000 m (3,281 ft) elevation, air density is approximately 1.112 kg/m3 (9% less than sea level). This means wind power at 1,000 m altitude is about 9% less than at sea level for the same wind speed. High-altitude wind farms must account for this reduction in power output.

What is the Betz limit for wind turbine efficiency?

The Betz limit, derived by Albert Betz in 1919 and published in 1920, states that no wind turbine can convert more than 16/27 (approximately 59.3%) of the kinetic energy of wind into mechanical energy. This theoretical maximum is called the Betz coefficient or Betz limit. Modern utility-scale wind turbines achieve power coefficients (Cp) of 0.40 to 0.50, approaching 85% of the Betz limit. The actual electrical output is further reduced by generator and gearbox losses.

Official sources

  • NREL Wind Resource Data and Tools: nrel.gov.
  • DOE Wind Energy Technologies Office: energy.gov.
  • ICAO Doc 7488, Manual of the ICAO Standard Atmosphere: icao.int.

Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.