Septic Tank Sizing

Minimum tank gallons from bedrooms or daily flow.

Run the calculator

Example

You enter

Bedrooms 4

You get

Daily flow 600 gpd
Minimum tank gallons 1200 gal
Floor gallons 1000

Details, formula, and sources

Tank capacity from EPA on-site wastewater treatment manual sizing rules and state minimum-volume tables; required volume = bedrooms × per-bedroom rule + safety reserve.

U.S. EPA Onsite Wastewater Treatment Systems Manual (EPA/625/R-00/008); state-published per-bedroom rules.

Free at epa.gov/septic. State rules free on each state department of health / DEQ site.

Estimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.

Field names used by the API: bedrooms, daily_flow_gpd, minimum_tank_gallons, floor_gallons

Per-bedroom rule from data/plumbing/septic-rules.json keyed to state when supplied; defaults to EPA manual minimums otherwisedata/plumbing/septic-rules.json