What Size Septic Tank Do I Need?

Bedrooms matter

Many residential rules use the number of bedrooms or bedroom equivalents because that approximates potential occupancy and wastewater flow. Boone County, Indiana, for example, publishes a design basis tied to 150 gallons per day per bedroom and the soil loading rate.

The tank is only one component

Drainfield area, dosing, pumps, treatment units, reserve area, soil conditions, and local setback rules may control the design even when the tank size itself is straightforward.

What to verify locally

Permitting, inspection, setbacks, acceptable system types, professional licensing, and design requirements are controlled by state and local authorities. If your question affects construction, a property purchase, a repair, or drinking-water safety, confirm the answer with the local health/environmental department.