Mechanical & Civil Engineering
Broad-Crested Weir Discharge Calculator
Calculate the discharge over a broad-crested weir given head and crest width.
Your inputs
Change any value to update the result instantly.
Discharge (Q)
1.1 m³/s
Unit discharge
0.367 m²/s
Head used
0.4 m
Discharge coefficient
0.85
What this calculator does
Broad-Crested Weir Discharge Calculator: Applies the standard civil and geotechnical relationship for this problem so the flow, pressure, settlement or capacity can be worked out from measured site inputs.
What your result means
The headline figure is the hydraulic or geotechnical quantity implied by your site inputs. Compare it against the design criteria in the applicable code before acting on it.
Formula and working
Q = Cd × (2/3) × √(2g/3) × b × H^1.5
- 1
Collect the inputs
Crest width (b) = 3 m; Upstream head (H) = 0.4 m; Discharge coefficient (Cd) = 0.85
- 2
Apply the formula
Q = Cd × (2/3) × √(2g/3) × b × H^1.5
- 3
Result
Discharge (Q) = 1.1 m³/s
Frequently asked questions
Symbols and assumptions
- crestWidth
- Crest width (b) (m)
- head
- Upstream head (H) (m)
- dischargeCoeff
- Discharge coefficient (Cd)
- • Steady-state, single-phase conditions are assumed unless the page says otherwise.
- • Site inputs (soil properties, flow, roughness) come from the user's own survey or testing.
Sources and review
Reviewed 2026-09-22 · Next review 2027-09-22
- • This is an educational estimate for learning and checking, not a design deliverable.
- • Real design must follow the governing code or standard for your jurisdiction and be reviewed and signed off by a qualified engineer.
- • Safety factors, load combinations and material certification are the responsibility of the designer, not of this page.
Important limitation
This is an educational estimate based only on the values and formula shown. Verify current rates, rules, units, and professional standards before relying on the result. It is not personalized financial or investment advice.
Report a mistake or request an improvement
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