Septic tank size calculator
Two modes: US sizing by bedrooms (typical state minimums) and Indian sizing by users (IS 2470 screening rule). Both are estimates — local code governs.
US tanks are sized by bedroom count because occupancy drives flow; most state codes set 1,000 gallons as the 3-bedroom minimum with steps of ~250 gal per extra bedroom. Indian practice under IS 2470 designs for sewage flow plus sludge accumulation between desludgings; the per-user screening figure here assumes a 2–3 year cycle. In both markets, percolation tests and the local authority decide the final installation.
FAQ
What size septic tank for a 3-bedroom house (US)?
1,000 gallons is the typical state minimum for 3 bedrooms; 1–2 bedrooms commonly 750–1,000 gal, 4 bedrooms 1,250 gal. Your county health department's table governs — always check it.
How is septic size worked out in India?
Design follows IS 2470: liquid retention for daily sewage flow plus a sludge zone sized to the desludging interval. The quick screening rule of ~250 L per user (minimum 1,000 L) approximates a 2–3 year desludging cycle — final design is per IS 2470 and your local PHE norms.
Is this calculator a design document?
No — it's a screening estimate. Septic design is regulated; soil percolation, water table and local code drive the real answer.