Enter the rated CFM of the fan and the diameter of the fan into the calculator to determine the fan velocity.

Fan Velocity Formula

The following equation is used to calculate the Fan Velocity.

Vfan = CFM / (pi*(D/12)^2/4) / 60

  • Where Vfan is the fan velocity (ft/s)
  • CFM is the rated cubic feet per minute of the fan (ft^3/min)
  • D is the diameter of the fan (in)

What is a Fan Velocity?


Fan velocity describes the speed at which a fan moves air through it’s blades.

How to Calculate Fan Velocity?

Example Problem:

The following example outlines the steps and information needed to calculate Fan Velocity.

First, determine the rated cubic feet per minute of the fan. In this example, the CFM is found to be 350.

Next, determine the diameter of the fan. For this problem, the diameter is found to be 10 inches.

Finally, calculate the Fan Velocity using the formula above:

Vfan = CFM / (pi*(D/12)^2/4) / 60

Vfan = 350 / (3.14159*(10/12)^2/4) / 60

Vfan = 10.695 ft/s