Common tools for this include digital apps from industry leaders like Price Industries or online calculators. If you can tell me:

I can help walk you through the calculation or direct you to a specific tool. Duct Pressure Loss Calculator | Plastec Ventilation

Proper sizing prevents noisy systems and ensures adequate air delivery to rooms.

The volume of air (CFM or L/s) passing through the fitting.

Helps ensure that the total pressure does not exceed the capacity of the air handling unit (AHU).

The speed of the air (FPM or m/s), which directly affects friction.

The calculator converts the resistance of a fitting into an equivalent length of straight duct, allowing for easier total pressure calculations.