A preliminary recommended septic tank size for residential use, based on number of users and cleaning interval — for up to 20 users.
For residential septic tanks serving up to 20 users.
The selected size corresponds to the recommended table value for up to 5 users.
Indicative household sizes commonly presented in CPHEEO guidance based on IS 2470 Part 1 assumptions.
| Users | Length (m) | Breadth (m) | Liquid depth — 2 yr (m) | Liquid depth — 3 yr (m) |
|---|---|---|---|---|
| 5 | 1.50 | 0.75 | 1.00 | 1.05 |
| 10 | 2.00 | 0.90 | 1.00 | 1.40 |
| 15 | 2.00 | 0.90 | 1.30 | 2.00 |
| 20 | 2.30 | 1.10 | 1.30 | 1.80 |
Simplified illustration only — not a construction drawing.
For up to 5 users, the reference table gives an internal plan size of about 1.50 m × 0.75 m, with 1.00 m liquid depth for a 2-year cleaning interval and 1.05 m for 3 years, plus 0.30 m freeboard.
No. Septic tank sizing and effluent disposal are separate design considerations. A soak pit or another permitted disposal/treatment arrangement must be selected based on soil, groundwater and local requirements.
This version is intentionally limited to small residential applications up to 20 users. A separate community/large septic tank estimator should be used for higher populations.
The dimensions shown are intended as internal tank dimensions. Wall and base thickness must be added separately according to the structural design and construction material.