Calculate CFM from differential pressure and area, or estimate duct airflow, velocity, and area from pressure plus rectangular or round duct size.

CFM from Differential Pressure Calculator

CFM / Area / Pressure
Duct Size Method

Enter any 2 values to calculate the missing variable.

CFM From Differential Pressure Formula

The following two example problems outline the steps and information needed to calculate the CFM From Differential Pressure.

CFM = 4005 * SQRT( dP) * A

Variables:

  • CFM is the CFM From Differential Pressure (ft^3/min)
  • dP is the differential pressure (W.C.) 
  • A is the cross-sectional area (ft^2) 

To calculate CFM from differential pressure, multiply the square root of the pressure by the area, then multiply again by 4005.

How to Calculate CFM From Differential Pressure?

The following steps outline how to calculate the CFM From Differential Pressure.

  1. First, determine the differential pressure (W.C.). 
  2. Next, determine the cross-sectional area (ft^2). 
  3. Next, gather the formula from above = CFM = 4005 * SQRT( dP) * A.
  4. Finally, calculate the CFM From Differential Pressure.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

differential pressure (W.C.) = .50

cross-sectional area (ft^2) = 2.5

CFM = 4005 * SQRT( dP) * A = ?