What CFM fan and duct evidence does this bathroom need?
Use HVI room or fixture demand for the target, but do not turn duct length into a made-up delivered-CFM percentage. Enter the route, flag resistance, then verify the chosen model at 0.1 and 0.25 in. w.g.
Method
The room target takes the higher of HVI area/fixture guidance and an 8-ACH high-ceiling check. Equivalent route is a labelled planning assumption, never an official fan curve.
Important limitation
Exact delivered airflow depends on the selected fan, duct fittings, cap, leakage and installation. The result cannot approve code compliance or product suitability.