The formula to calculate Specific Speed (Ns) is:

\[ Ns = \frac{N \cdot Q^{0.5}}{Ps^{0.75}} \]

Where:

• \(Ns\) is the specific speed (dimensionless).
• \(N\) is the speed of the air moving unit (rpm).
• \(Q\) is the airflow (cfm).
• \(Ps\) is the pressure requirement (in. H2O).