Operator calculator
Surface Overflow Rate calculator
Divide flow in gpd by a circular clarifier's surface area.
Calculator
Surface overflow rate
424.4 gpd/ft²
- 1. Area = π × 60² ÷ 4 = 2,827.4 ft²
- 2. 1.2 MGD × 1,000,000 = 1,200,000 gpd
- 3. 1,200,000 gpd ÷ 2,827.4 ft² = 424.4 gpd/ft²
For instructional use. Results assume the standard conversion factors shown on this page. Actual field calculations may need chemical strength, density, temperature, and other adjustments, so check your plant’s procedures.
Formula and inputs
SOR (gpd/ft²) = flow (gpd) ÷ [0.785 × diameter² (ft²)], with flow (gpd) = MGD × 1,000,000
| Input | Unit |
|---|---|
| Flow | MGD |
| Clarifier diameter | ft |
| Result: Surface overflow rate | gpd/ft² |
Conversion factors used: 1 MGD = 1,000,000 gpd; area of a circle = π × d² ÷ 4 (about 0.785 × d²).
When to use it
Surface overflow rate compares flow to the surface area of a clarifier. It is the rise rate particles must beat to settle, so lower is better for settling.
For a circular tank, find the area from the diameter first. Keep π and the square in the area calculation.
Applies to: Water Treatment, Wastewater Treatment.
Exam tip: Diameter is not radius. If the problem gives radius, double it first.
Study guides
Build the math skill behind the calculator
Water Operator Math Made Simple walks through the formulas step by step.
Water Operator Math Made Simple
A Step-by-Step Guide to the Math Every Water Operator Needs to Know