The speed of the air (FPM or m/s), which directly affects friction.
The volume of air (CFM or L/s) passing through the fitting. duct fitting loss calculator
Specifically identifying if it's a 90-degree elbow, a tee, or a reducing transition. Why You Should Use One The speed of the air (FPM or m/s),
Common tools for this include digital apps from industry leaders like Price Industries or online calculators. If you can tell me: duct fitting loss calculator