Skip to content
ENExplore Calculators

Fan Power Calculator

Work out fan power instantly with clear inputs, formula shown and shareable results.

About Fan Power Calculator

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.

Formulas

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

Worked example

With the default values below, Fan Power Calculator returns Fan shaft power of 1.452. Change any input above and every figure here is recalculated in your browser.

Inputs used

Airflowminimum 1 CFM
4,000 CFM
Total static pressureminimum 0.05 in.wg
1.5 in.wg
Fan total efficiencyaccepts 10–95 %
65 %
Motor and drive efficiencyaccepts 30–100 %
90 %

Results

Fan shaft power
1.452 bhp
Shaft power in kilowatts
1.083 kW
Electrical input power
1.203 kW
Specific fan power
0.301 W/CFM

Step by step

  1. 1Values used
  2. 2Brake horsepower
  3. 3Input power
  4. 4Fan shaft power= 1.452 bhp
  5. 5Shaft power in kilowatts= 1.083 kW
  6. 6Electrical input power= 1.203 kW
  7. 7Specific fan power= 0.301 W/CFM

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Fan Power figure worked out?

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.

Why is specific fan power regulated?

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.

What values do I need to enter?

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.

Related Calculators

Fan Power Calculator – Calculate Fan shaft power | Calcrivo