Air Horsepower Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026The theoretical baseline for fan sizing
Air horsepower is the minimum theoretical power needed to move a given volume of air against a given resistance, assuming a perfectly efficient fan with no losses - real fans always require more input power than this figure due to mechanical and aerodynamic inefficiencies.
Worked example
For 2,000 CFM moved against 1.5 in. w.g. of static pressure:
AHP = (2,000 x 1.5) / 6356 = 0.472 hp
Real fans typically run at 50-70% efficiency, so the actual motor size needed is this air horsepower figure divided by the fan's efficiency rating - for the example above, a fan at 60% efficiency would need roughly 0.79 hp of actual motor power, not the theoretical 0.472 hp.