I can help walk you through the calculation or direct you to a specific tool. Duct Pressure Loss Calculator | Plastec Ventilation
The volume of air (CFM or L/s) passing through the fitting. duct fitting loss calculator
By accurately sizing fans, you prevent over-pressurizing the system, which wastes energy. I can help walk you through the calculation
Specifically identifying if it's a 90-degree elbow, a tee, or a reducing transition. Why You Should Use One you prevent over-pressurizing the system
The diameter (round) or height and width (rectangular) of the duct.