Broad Crested Weir Calculator

Find flow over a broad-crested weir.

Discharge coefficient

Weir width

Head

Gravity (m/s²)

Flow rate (m³/s) 1.1

Formula: Q = Cd·(2/3)^(3/2)·√g·b·H^(3/2)

Step-by-step with your numbers:

1. Values used:

2. Discharge coefficient = 0.85

3. Weir width = 3

4. Head = 0.4

5. Gravity = 9.81 m/s²

7. Flow rate = 1.1m³/s

Did we solve your problem today?

A broad-crested weir is a flat-topped barrier used to measure open-channel flow.

The math behind it

Q = Cd·(2/3)^(3/2)·√g·b·H^(3/2). Flow grows with the 3/2 power of the head.

Cd 0.85, 3 m wide, 0.4 m head → about 1.16 m³/s.

Why measure with a weir?

Flow depends only on the easily measured head over the crest.