### Formula

Dh

hydraulic diameter of the pipe

A

cross-sectional area (of the fluid)

P

wetted perimeter (the length of the water exposed to air is NOT included)

Dh

hydraulic diameter of the pipe

A

cross-sectional area (of the fluid)

P

wetted perimeter (the length of the water exposed to air is NOT included)

For shapes such as squares, rectangular or annular ducts (where the height and width are comparable) the characteristic dimension for internal flow situations is taken to be the hydraulic diameter.

A

P

Dh

Precision

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