This fan power calculator turns airflow and total static pressure into the numbers you need to size a fan and its motor. Enter the airflow in CFM, the total static pressure in inches of water column, and the fan, motor, and drive efficiencies, then pick the supply voltage. The tool returns air horsepower, brake horsepower, the next standard NEMA motor size, input kW, estimated full load amps, overall wire-to-air efficiency, specific fan power, and annual energy.
Fan power is often the largest single electrical load in an air system, so getting brake horsepower and motor selection right drives both first cost and operating cost. The specific fan power (W/CFM) result gives a fast efficiency check, and the calculator flags values that should be verified against · ASHRAE 90.1 fan power limits.
| Air horsepower | AHP = CFM × TSP ÷ 6,356 |
| Brake horsepower | BHP = AHP ÷ ηfan |
| Input power | kW = BHP × 0.7457 ÷ (ηmotor · ηdrive) |
| Specific fan power | SFP = kW × 1,000 ÷ CFM (W/CFM) |
| Full load amps (3Ø) | FLA = kW × 1,000 ÷ (√3 · V · PF) |
The constant 6,356 = 33,000 ft·lbf/min per HP ÷ 5.192 lbf/ft² per inch of water column, and it converts CFM × in.w.c. directly into horsepower. The factor 0.7457 converts horsepower to kilowatts. Motor size snaps up to the next standard NEMA rating, and the full-load-amp estimate uses an assumed 0.85 power factor (single-phase drops the √3 term and divides by motor efficiency). These relationships follow standard ASHRAE and NEMA fan and motor practice; verify specific fan power against ASHRAE 90.1 fan power limits.