Wind Energy Density Calculator
Compute the power available per square metre of wind-swept area at a given location. Engineers and site assessors use this metric to compare potential wind farm sites before committing to infrastructure.
About this calculator
Wind power density (WPD) quantifies how much energy the wind carries through a unit cross-sectional area per second. The formula is WPD = 0.5 × ρ × v³, where ρ is air density in kg/m³ and v is wind speed in m/s. The result is expressed in watts per square metre (W/m²). Because power scales with the cube of wind speed, small differences in average speed produce large differences in energy density—a 10% increase in wind speed yields roughly 33% more energy density. Standard air density at sea level is 1.225 kg/m³, but sites at high altitude or in extreme climates require adjusted values. Wind power density classes range from Class 1 (poor, <100 W/m²) to Class 7 (superb, >800 W/m²), and this metric is the primary screening tool used in the U.S. Wind Resource Atlas.
How to use
Assume a coastal site with an average wind speed of 7 m/s and air density of 1.225 kg/m³. Step 1 — Cube the wind speed: 7³ = 343 m³/s³. Step 2 — Multiply: 0.5 × 1.225 × 343 = 210.2 W/m². Enter 7 m/s and 1.225 kg/m³ into the calculator to get approximately 210 W/m². This falls in Wind Power Class 3, which is considered suitable for utility-scale development. Comparing this value across multiple candidate sites quickly identifies the most energy-rich location.
Frequently asked questions
What is a good wind energy density value for a viable wind farm site?
Sites with a wind power density above 200 W/m² (Class 3 or higher) are generally considered viable for utility-scale wind farms. Class 4 sites (300–400 W/m²) are preferred, and Class 6–7 sites (600 W/m² and above) are considered excellent. Values below 100 W/m² are typically not economical for large turbines, though small residential turbines may still be worthwhile. Most developers require at least 12–18 months of on-site wind measurement before making a final investment decision.
How does air density affect wind energy density calculations?
Air density directly multiplies the result, so a 5% reduction in density reduces wind power density by exactly 5%. At an elevation of 1,500 m, air density is roughly 1.058 kg/m³ instead of 1.225 kg/m³, which reduces available power by about 14%. Cold, dry air is denser than warm, humid air, so winter months in temperate climates often show higher energy density despite similar wind speeds. Always use a site-specific or elevation-adjusted air density for accurate resource assessments.
What is the difference between wind energy density and wind turbine power output?
Wind energy density measures the theoretical power available in the wind per square metre of area—it is a property of the wind resource itself, independent of any machine. Wind turbine power output measures how much of that resource a specific turbine actually converts to electricity, accounting for rotor swept area and turbine efficiency. Energy density is used to compare sites and screen locations, while turbine power output is used to size equipment and forecast generation. You need both figures for a complete project feasibility study.