Weir Flow Rate Calculator

Summary

Enter weir type and head height to instantly calculate volumetric flow rate using standard hydraulic formulas.

How it works

1. Select the weir type: rectangular, triangular (V-notch), or trapezoidal.
2. Enter the weir crest length (for rectangular or trapezoidal) or the notch angle (for V-notch).
3. Enter the head of water above the weir crest in your preferred unit.
4. The calculator applies the standard discharge coefficient and formula for the selected weir type.
5. Flow rate is displayed in m³/s, ft³/s, and liters per second.

Use cases

• Sizing weirs for irrigation canals and farm water management.
• Measuring stream flow in hydrological field surveys.
• Designing stormwater outlet structures for retention ponds.
• Checking weir capacity for wastewater treatment overflow.
• Teaching hydraulics — verify hand calculations instantly.
• Estimating flow in open-channel drainage systems.

Frequently Asked Questions