Broad-Crested & Sharp-Crested Weir (Full Suite)

Discharge, modular ratio, submergence correction and flow-regime auto-detection. Supports SI (m, m³/s) and US (ft, ft³/s) units.

Weirs & Orifices · Advanced Modular ratio Submergence correction Auto regime detection Rectangular & V-notch

Input Parameters

Choose weir type & unit system, then enter heads and crest length. Coefficients have reasonable defaults but are user-editable for calibration.

Weir & units
Geometry & heads
Discharge coefficients

For rectangular & broad weirs: Q = C · L · H₁3/2 (C already includes constants).
For V-notch (90°): Q = C · H₁2.47 with C pre-set for typical 90° notches. Modular ratio m = Q / Qideal.

Results & Exports

Submergence ratio –
Correction factor (Villemonte) –
Ideal discharge Qideal (m³/s) –
Corrected discharge Q (m³/s) –
Modular ratio m –

Q values are in m³/s. For submerged conditions, a Villemonte-type relation is applied: Q = Qfree · (1 − (H₂/H₁)1.5)0.385. Critical submergence threshold depends on weir type.

0 records Calculation history
# Weir type Mode L (m) H₁ (m) H₂ (m) Cideal Cused Sub. ratio H₂/H₁ Flow regime Qideal (m³/s) Qfree,used (m³/s) Qcorr (m³/s) m = Q/Qideal
This tool is intended for engineering calculations and quick checks. For critical design, always cross-check with your project’s governing standards and more detailed hydraulics analysis.

Reference Schematic (not to scale)

Generic profile showing upstream head H₁, downstream head H₂ and crest length L. V-notch mode assumes a 90° triangular opening.

H₁ H₂ L Flow →