Hydraulics & drainage · Pipes & hydraulic structures
Weir discharge (sharp & broad crested) calculator
Rectangular sharp-crested weir Q = Cd(2/3)√(2g) b H^1.5 and broad-crested Q = 1.705 b H^1.5.
Standard: Standard weir equations
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Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Crest length | 3 | m |
| Head over crest | 0.4 | m |
| Sharp-crested Cd | 0.62 |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Sharp-crested Q | 1.39 | m³/s |
| Broad-crested Q | 1.29 | m³/s |
- ✓ Head > 0.03 m (valid range)
Method, formulas and assumptions
- Sharp-crested Q = 0.62*2/3*SQRT(2*9.81)*3*0.4^1.5 = 1.3895 m³/s
- Broad-crested Q = 1.705*3*0.4^1.5 = 1.294 m³/s
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.