Small Wind Turbine Sizing Calculator

A typical US home consumes around 10,500 kWh per year (~30 kWh/day). Depending on your average wind speed, a residential turbine with a rotor diameter of 5–8 m and a rated output of 5–15 kW can often cover a large portion of that demand. Use this calculator to match turbine size to your actual consumption by entering your daily energy use and local wind conditions.

Power is calculated using the formula P = ½ × ρ × A × v³ × Cp, where ρ is air density (kg/m³), A is the rotor swept area (m²), v is wind speed (m/s), and Cp is the coefficient of performance. Because wind speed is cubed, even a small increase in wind speed significantly boosts power output.

The coefficient of performance (Cp) measures how efficiently a turbine converts wind kinetic energy into electrical power. The theoretical maximum — known as the Betz limit — is 0.593. Most small residential turbines achieve a Cp between 0.25 and 0.45 in real-world conditions.

Horizontal-axis wind turbines (HAWT) have blades that spin around a horizontal shaft facing the wind — these are the most common and efficient design for residential and utility-scale use. Vertical-axis wind turbines (VAWT) rotate around a vertical shaft and can capture wind from any direction, making them suitable for turbulent urban environments, though they are generally less efficient than HAWTs.

Denser air carries more kinetic energy, so turbines produce more power at sea level where air density is approximately 1.225 kg/m³. At higher altitudes or in hotter climates, air density drops, reducing power output. If your site is significantly above sea level, adjust the air density input accordingly — a decrease of roughly 0.001 kg/m³ per 10 m of altitude is a useful approximation.

Daily production depends on turbine size, wind speed, and how many hours per day the wind blows at a useful speed. For example, a 3 m diameter turbine with Cp = 0.35 operating at 7 m/s for 6 hours/day will produce roughly 3–4 kWh per day. Enter your specific parameters above to get a tailored estimate.

Most small wind turbines require a minimum average wind speed of around 4–5 m/s (9–11 mph) to be economically viable. Sites with average speeds below 4 m/s are generally not cost-effective for wind energy. Ideal residential sites typically see average speeds of 6 m/s or more at hub height.

The swept area is the circular area traced by the rotating blades, calculated as A = π × (D/2)². A larger swept area intercepts more wind, directly increasing power output. Doubling the rotor diameter quadruples the swept area, making rotor size one of the most influential factors in turbine performance.