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Weir & Orifice Flow

Discharge from sharp-crested rectangular & V-notch weirs, broad-crested weirs and free-flow orifices — instant Q for any geometry.

Inputs

m
m
m (0 if Rehbock unknown)
leave blank for default
Equations
  • Rectangular sharp-crested: Q = (2/3)·Cd·b·√(2g)·H3/2; default Cd ≈ 0.62 (Rehbock if P given).
  • V-notch: Q = (8/15)·Cd·tan(θ/2)·√(2g)·H5/2; default Cd ≈ 0.58.
  • Broad-crested: Q = Cd·b·H3/2·√(g·(2/3)3); default Cd ≈ 1.0 (in metric form Q = 1.7·b·H1.5).
  • Orifice: Q = Cd·A·√(2gh); default Cd ≈ 0.62.
  • Imperial: same form, with g = 32.174 ft/s².

Results

Type
Cd used
Discharge Q
Q (alt)