Septic Tank Size Calculator India (IS 2470)

Calculate Your Septic Tank Size

Enter household details and get capacity plus practical internal dimensions

Number of Users People living in the house. For 25+ users, ask us for community-scale design

What Drains to the Tank?

Wastewater per Person per Day (L) Toilet only: 40-50 L. All wastewater: 90-130 L

Desludging Interval

Liquid Depth 0.3 m freeboard is added on top

Length to Width Ratio Length should be 2-4 times the width

Recommended Internal Tank Size (L × W × Total Depth)

0 × 0 × 0 m

Required Liquid Capacity 0 L

Provided Liquid Capacity 0 L

Liquid Depth + Freeboard 0 m + 0.3 m

Serves 0 users

What Fills the Required Capacity

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Sizing uses IS 2470 based methodology with a 24 hour detention period, sludge storage of about 70 liters per person per year, minimum internal width of 0.75 m, minimum liquid depth of 1.0 m and 0.3 m freeboard, as of August 2026. Dimensions shown are internal clear sizes; excavation and outer size increase with wall thickness. Effluent must discharge to a properly sized soak pit. Final design depends on soil, water table and local body rules. Planning a full build on the plot? Estimate your project with our construction cost calculator.

Common Septic Tank Sizes by Number of Users

Indicative sizes from commonly used IS 2470 based recommendations

Users	Length × Width (m)	Liquid Depth (m)	Liquid Capacity (approx.)
5 users	1.5 × 0.75	1.0	1,125 liters
10 users	2.0 × 0.90	1.0	1,800 liters
15 users	2.0 × 0.90	1.3	2,340 liters
20 users	2.3 × 1.10	1.3	3,290 liters

Indicative reference for toilet-waste tanks with regular desludging; add 0.3 m freeboard above liquid depth. Tanks receiving all household wastewater need roughly double the capacity. Verify final sizing against your drawings and local requirements.

How This Calculator Works

The tank must hold one day of incoming wastewater long enough for solids to settle, plus the sludge that accumulates between cleanings. That is exactly how the calculator sizes it, using the same logic as IS 2470 based design practice.

Required Capacity = (Users × Liters per Person per Day × 1 Day) + (Users × 70 L per Year × Desludging Years)
Dimensions: Area = Capacity ÷ Liquid Depth, with Length = 2-4 × Width

The calculator then applies practical minimums: at least 1,000 liters of liquid capacity, internal width of at least 0.75 m, liquid depth of at least 1.0 m and a 0.3 m freeboard above the liquid level. If a constraint kicks in, the provided capacity shown will be higher than the bare requirement, which is the safe direction.

Two Compartments Work Better

Tanks are commonly built with two chambers, the first about two-thirds of the length, which improves settling and keeps the outlet cleaner.

Soak Pit Is Mandatory

Effluent leaving the tank must go to a soak pit or dispersion trench sized to your soil's percolation, never to an open drain.

We Design and Build It

Brick or RCC construction, ventilation pipe, access covers, inlet and outlet tees, and the soak pit, executed as part of your project or standalone.

Residential construction with septic tank work by Sujeet Engineering Solutions

400+

Structures Built

100%

Quality Tested

Frequently Asked Questions

Common questions about septic tank sizing and construction

What size septic tank do I need for a family of 5?

A family of 5 typically needs a liquid capacity of about 1,100-1,300 liters, which works out to an internal size of roughly 1.5m long, 0.75m wide and 1.0m liquid depth, plus 0.3m freeboard on top. If all household wastewater drains to the tank rather than toilet waste alone, size it toward the higher end or larger.

How is septic tank size calculated?

Required capacity equals daily wastewater flow (users multiplied by liters per person per day) held for a detention period of about 24 hours, plus sludge storage of roughly 70 liters per person per year multiplied by the years between cleanings. The volume is then converted into length, width and depth, keeping length 2-4 times the width, minimum width 0.75m and minimum liquid depth 1.0m.

What is the minimum size of a septic tank?

Practical minimums from IS 2470 based guidance are about 1,000 liters of liquid capacity, an internal width of at least 0.75m, a liquid depth of at least 1.0m and a freeboard of 0.3m above the liquid level. Even for very small households, the tank should not be built smaller than this.

How often should a septic tank be cleaned?

Household septic tanks are typically desludged every 1-2 years. The interval you plan for directly affects tank size: a tank designed for cleaning every 2 years needs roughly double the sludge storage of one cleaned annually, which is why this calculator asks for your desludging interval.

Do I need a soak pit with a septic tank?

Yes. Septic tank effluent is only partially treated and must discharge into a soak pit or dispersion trench, never into an open drain. Soak pit size depends on soil percolation at your plot, which is assessed during design. Our team designs and constructs the tank and soak pit together.

Should the tank take toilet waste only or all household wastewater?

Both designs are used. A toilet-only tank receives about 40-50 liters per person per day, while a tank receiving all household wastewater including bath and kitchen sees roughly 90-130 liters per person per day, so it needs to be about twice the size. The calculator lets you pick either mode and edit the flow figure.

Is a septic tank required in Delhi NCR?

In sewered colonies you connect directly to the municipal sewer and no septic tank is needed. Septic tanks are used on unsewered peripheral plots, farmhouses and sites where the sewer line has not yet arrived, subject to local body rules. Sujeet Engineering Solutions handles the design, approvals context and construction as part of residential projects across Delhi NCR.

Septic Tank Size Calculator (IS 2470 Based)