Sedimentation Tank Sizing Calculator

Work out sedimentation tank sizing instantly with clear inputs, formula shown and shareable results.

About Sedimentation Tank Sizing Calculator

Sedimentation basins are sized on surface overflow rate, since settling depends on surface area rather than volume — a particle settles if its settling velocity exceeds the overflow rate. Detention time then fixes the volume and hence the depth. Typical values are 20-40 m3/m2/day and 2-4 hours for water treatment.

Formulas

Surface area

Area = flow / surface overflow rate

Volume and depth

Volume = flow x detention time / 24; depth = volume / area

Worked example

With the default values below, Sedimentation Tank Sizing Calculator returns Surface Area Required of 333.33. Change any input above and every figure here is recalculated in your browser.

Inputs used

Design Flowminimum 0 m3/day: 10,000 m3/day
Surface Overflow Rateminimum 0 m3/m2/day: 30 m3/m2/day
Detention Timeminimum 0 hours: 2.5 hours
Length To Width Ratiominimum 0.1: 4

Results

Surface Area Required: 333.33
Tank Volume: 1,041.67
Water Depth: 3.125
Tank Length: 36.515

Step by step

1Values used
2Surface area
3Volume and depth
4Surface Area Required= 333.33
5Tank Volume= 1,041.67
6Water Depth= 3.125
7Tank Length= 36.515

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is surface area more important than depth?

Ideal settling theory shows that removal depends only on the ratio of settling velocity to overflow rate. Depth affects detention time and scour resistance but not, in theory, the critical particle size removed.

What is short-circuiting?

Flow taking a direct path from inlet to outlet, so the effective detention time is far below theoretical. Inlet baffles, proper outlet weirs and tracer testing are used to control and verify it.