The calculator determines the friction factor ($\lambda$) based on the Reynolds Number ($Re$) and the relative roughness of the pipe material:
An "SF pressure drop" calculator estimates pressure loss for air/gas flow through a duct or pipe using the Darcy–Weisbach or empirical friction-factor methods where SF likely stands for "square feet" (ft²) cross-sectional area, "scale factor", or a specific software/standard shorthand. Commonly used inputs: sf pressure drop online-calculator
For fittings and valves, the calculator employs the "K-factor" or "Zeta-value" method: $$ \Delta P_fittings = \zeta \cdot \frac\rho v^22 $$ The tool aggregates these losses to provide a Total Dynamic Head (TDH) or total pressure drop. sf pressure drop online-calculator