Work out fan power instantly with clear inputs, formula shown and shareable results.
Fan air power is flow times pressure; dividing by fan efficiency gives shaft brake horsepower, and the constant 6356 converts CFM and inches of water gauge into horsepower. Dividing shaft power by motor and drive efficiency gives the electrical draw, and watts per CFM is the specific fan power that energy codes limit.
Brake horsepower
bhp = CFM x SP / (6356 x fan efficiency)
Input power
kW input = bhp x 0.7457 / motor efficiency; W/CFM = W input / CFM
bhp = CFM x SP / (6356 x fan efficiency). Fan air power is flow times pressure; dividing by fan efficiency gives shaft brake horsepower, and the constant 6356 converts CFM and inches of water gauge into horsepower.
Fans run for thousands of hours a year, so a small reduction in watts per CFM compounds. Many codes cap supply-plus-extract specific fan power for exactly that reason.
This calculator takes 4 inputs: Airflow, Total static pressure, Fan total efficiency, Motor and drive efficiency. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.