Calculator · Fluid Mechanics
Hydraulic Diameter Calculator
The hydraulic diameter is the length scale a non-circular duct presents to internal flow. It is four times the flow area divided by the wetted perimeter, and for a full circular pipe it is exactly the diameter.
Inputs
Results
Hydraulic diameter D_h = 4A/P_w
0.13333 m
| Flow area A | 0.02 m² |
|---|---|
| Hydraulic diameter D_h | 0.13333 m |
Explore in the Lab
Use this hydraulic diameter in the Pipe Flow Lab
The Lab characterises every segment by its hydraulic diameter.
Technical reference
D_h = 4 A / P_w
circular: D_h = D
rectangle w × h: D_h = 2wh / (w + h)
- D_h
- hydraulic diameter[m]
- A
- cross-sectional flow area[m²]
- P_w
- wetted perimeter of the section[m]
The wetted perimeter is not automatically the whole geometric perimeter: only the boundary in contact with the flowing fluid counts.
The hydraulic diameter is a length scale for Reynolds number and Darcy–Weisbach. It does not make a non-circular duct behave exactly like a round pipe.
Reference case: a 0.2 m × 0.1 m rectangle gives D_h = 0.133333… m.