MAXScanner thermal & fluid engineering
Hydraulic Diameter Calculator — Non-Circular Ducts & Channels
Calculate hydraulic diameter from flow area and wetted perimeter, with direct rectangular-duct support.
Last updated: September 17, 2026
Results
Enter positive dimensions
Formula, example and assumptions
D_h=4A/P_w; rectangle D_h=2ab/(a+b).
A 0.4 m × 0.2 m full rectangular duct has Dh≈0.267 m.
- Wetted perimeter includes only boundaries in contact with the fluid.
- Hydraulic diameter is a modeling length, not necessarily a geometric diameter.
Frequently asked questions
Why use hydraulic diameter?
It lets many internal-flow correlations extend to non-circular passages.
Does it equal pipe diameter?
For a full circular pipe, 4A/P simplifies exactly to the physical diameter.