Estimate kilowatts and full-time yearly kWh from flow, fall height, and turbine efficiency.
| kW | – |
| kWh / year (full time) | – |
Use this calculator for a mill, a mountain stream, or a textbook example when you know cubic metres per second and how far the water drops.
Power in kW = 9.81 × flow × fall height × efficiency. That 9.81 is gravity with water density already folded in (1,000 kg/m³ × 9.81 m/s² / 1,000). Fall height can be entered in metres (m) or feet (ft); it is converted to metres before the formula. Flow stays in cubic metres per second. Yearly kWh assumes the plant runs every hour of the year; if it does not, multiply by a capacity factor yourself. Efficiency is 0–1 (0.85 is a decent turbine).
Flow (m³/s): Water through the turbine in cubic metres per second. A small mill might be 1–10 m³/s.
Fall height: How far the water falls from intake to turbine, in m or ft. 20 m is a modest site.
Efficiency (0–1): Turbine and generator efficiency as a fraction. 0.85 means 85% of the water’s power becomes electricity.
kW: Instantaneous electrical power.
kWh / year (full time): Energy if the plant ran 8,760 hours.
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