Free Online Orifice Flow Calculator

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Orifice Flow — Free or Submerged


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Inputs
X
X
X
X
X
X
Results
Centroid elevation Centroid elevation X
Effective head, h ? Effective head, h ? X
Opening area, A Opening area, A X
Flow, Q Flow, Q X
Orifice regime check Orifice regime check X

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Notes

Orifice Equation
Q = Cd × A × √(2gh). For free outfall: h = HWE − centroid. For submerged flow (TWE above invert): h = HWE − TWE.
Orifice Regime
Orifice flow equations apply when the headwater surface is above the crown (top) of the opening. When headwater is below the crown, use a weir equation instead.
Discharge Coefficient
Cd ranges from about 0.60–0.65 for sharp-edged orifices. Rounded or re-entrant inlets use different values. See the Engineering Toolbox or the HEC-RAS Hydraulic Reference Manual for guidance.
Submergence
When TWE is above the opening invert, this calculator automatically applies the submerged orifice equation using h = HWE − TWE. When TWE is at or below the invert, free outfall is assumed and h = HWE − centroid.
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