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Calculators / Weir Overflow Rate

Weir Overflow Rate calculator

Weir overflow rate is flow divided by the length of weir the water spills over. For a weir around the edge of a circular clarifier, length = π × diameter.

WOR (gpd/ft) = Flow (gpd) ÷ Weir length (ft)
Weir length = 3.1416 × D

    Worked example

    A circular clarifier has a 60 ft diameter weir and receives 2,000,000 gpd. What is the weir overflow rate?

    1. Weir length = 3.1416 × 60 = 188.5 ft
    2. WOR = 2,000,000 ÷ 188.5 = 10,610 gpd/ft

    Answer: 10,610 gpd/ft

    Common mistakes

    • Using area (0.785 × D²) instead of circumference (π × D).

    Check your exam's reference sheet for its exact constants. Some use 3.14 instead of 3.1416, which changes answers in the last digit.