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).