# Hydraulic Diameter

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

Hydraulic diameter, abbreviated as $$d_h$$, is normally used when the flow is in non-circular pipe or tubes and channels.  Circular pipe has the same pressure drop of a rectangular channel but a greater average velocity.  Square or rectangular pipes have a greater weight and a greater pressure drop compared with a circular pipe with the same section.  For established shapes, various calculations are linked below.

## hydraulic diameter formula

 $$\large{ d_h = \frac { 4 \; A_c } { P } }$$

### Where:

 Units English Metric $$\large{ d_h }$$ = hydraulic diameter $$\large{ ft }$$ $$\large{ m }$$ $$\large{ A_c }$$ = area cross-section of flow $$\large{ ft^2 }$$ $$\large{ m^2 }$$ $$\large{ P }$$ = wetting perimeter cross-section $$\large{ ft }$$ $$\large{ m }$$

## Hydraulic Diameters for Specific Flow Profiles Hydraulic Diameter for pipe flow profile Hydraulic Diameter for annular flow profile Hydraulic Diameter for ellipse Hydraulic Diameter for square tube Hydraulic Diameter for rectangular tube Hydraulidc Diameter for isosceles triangle Hydraulic Diameter for right triangle