Wind Resource Assessment Calculator
Wind resource assessment is the process of evaluating how much usable wind energy a site actually holds — the foundation of every wind project decision, from feasibility to financing. This calculator takes your measured average wind speed, measurement height, and air density, then reports wind power density in W/m2 and assigns an NREL wind resource class from 1 (Poor) to 7 (Superb) using the standard classification bands developed for decades of U.S. wind resource mapping. Because power density scales with the cube of wind speed, the class captures far more than a single speed reading. Pair the result with our Wind Power Density Calculator to see the underlying energy-per-area math, and our Capacity Factor vs. Hub Height Calculator to adjust a wind speed measured at one height up to your target hub height before classifying.
The average wind speed at your measurement height, typically from an on-site meteorological tower or anemometer. Power density scales with the cube of wind speed, so this input dominates the result.
50m is NREL's standard reference height for wind power classification, even though most modern turbine hub heights are taller.
1.225 kg/m3 is standard sea-level air density at 15C. Air density decreases with altitude and increases at lower temperatures.
0.5 × air density (kg/m3) × measured average wind speed (m/s)^3
NREL wind power classification at a 50m reference height (Class 1 Poor < 200 W/m2 … Class 7 Superb > 800 W/m2)
This uses NREL's classic wind power classification bands, standardized at a 50m reference height. If your measured wind speed is from a different height, use the Capacity Factor vs. Hub Height Calculator first to adjust to 50m (or your target height) before classifying.
Results update live as you type. For planning and field-check estimates — always verify against applicable standards and equipment ratings.
How we calculate this →NREL's wind power classification system, developed and used for decades of U.S. wind resource assessment, sorts sites into seven classes based on power density at a standard reference height -- from Class 1 (poor, under 200 W/m2) to Class 7 (superb, over 800 W/m2). Most commercially developed U.S. wind farms sit in the Class 3-5 range. An 8 m/s average wind speed at 50m lands right at 314 W/m2, squarely in Class 3 (Fair) -- a genuinely developable resource, though not among the best sites in the country.
How wind resource assessment is calculated
This calculator estimates a site's wind power density and assigns an NREL wind resource class, tying three inputs together: the measured average wind speed, the measurement height, and the air density. Two quantities tie the calculation together.
Power Density (W/m2) = 0.5 × Air Density (kg/m3) × Measured Average Wind Speed (m/s)^3. The power available in moving air comes from its kinetic energy flux: the mass of air moving through a given area per unit of time (proportional to wind speed) multiplied by the kinetic energy per unit of mass (proportional to wind speed squared). Combining these gives a cubic relationship -- power scales with the cube of wind speed. Air density sets the mass term: higher density means more mass of air moving at a given speed, directly increasing power density. At the defaults (8.0 m/s, 1.225 kg/m3), that is 0.5 × 1.225 × 8.0^3 = 0.5 × 1.225 × 512 = 313.6 ≈ 314 W/m2.
Wind Resource Class = NREL classification band applied to the power density at a 50m reference height. NREL's seven-class system sorts wind resource quality from Class 1 (Poor, under 200 W/m2) through Class 2 (Marginal, 200–300 W/m2), Class 3 (Fair, 300–400 W/m2), Class 4 (Good, 400–500 W/m2), Class 5 (Excellent, 500–600 W/m2), Class 6 (Outstanding, 600–800 W/m2), up to Class 7 (Superb, over 800 W/m2). At the default 314 W/m2, the site falls into Class 3 (Fair) -- a genuinely developable resource, though not among the best sites in the country.
Two notes on the model. First, the classification bands are standardized at a 50m reference height, which predates the era of 100m+ hub heights common today but remains the conventional reference for comparing wind classification data across historical resource maps and studies. If your measured wind speed comes from a different height, adjust it to 50m (or your target height) using the wind shear power law in the Capacity Factor vs. Hub Height Calculator before classifying. Second, this calculator uses a single average wind speed; real wind resource assessment is far more rigorous, typically using on-site meteorological towers or remote sensing devices (LIDAR or SODAR) collecting wind speed and direction data across a full year or more, combined with modeling that accounts for terrain, roughness, and long-term climate correlation. Data sources: NREL wind power classification system from NREL wind resource assessment methodology and U.S. wind resource mapping; wind power density formula from wind physics and kinetic energy principles; wind resource class definitions and thresholds from NREL's Wind Energy Resource Atlas and wind resource assessment standards; commercial wind farm development data from utility-scale wind project case studies and regional transmission operator reports; meteorological tower and LIDAR wind resource assessment methodologies from wind energy engineering standards and professional assessment practices. Verification: with defaults (8.0 m/s, 50m, 1.225 kg/m3), Power Density = 314 W/m2, Wind Resource Class = Class 3 — Fair.