The hydraulic diameter of a non-circular conduit is defined as four times the cross-sectional area divided by the wetted perimeter. It represents an equivalent diameter of a circular conduit that would have the same flow resistance as the non-circular conduit. The hydraulic diameter () is typically expressed in meters (m). The formula for calculating the hydraulic diameter () depends on the shape of the conduit:
Where:
- is the hydraulic diameter,
- Area is the cross-sectional area of the conduit,
- Wetted Perimeter is the perimeter of the conduit in contact with the fluid.