Septic tank size by state / East North Central
Indiana septic tank size
In Indiana the minimum septic tank for a three-bedroom house is 1,000 gallons, rising to 1,250 gallons at four bedrooms. The figure comes from 410 IAC 6-8.3-60(c), Table III (Residential On-Site Sewage Systems). That matches the 1,000-gallon median of the 47 states listed here.
What the Indiana rule says
The rule is 410 IAC 6-8.3-60(c), Table III (Residential On-Site Sewage Systems); design flow 410 IAC 6-8.3-12, administered by Indiana Department of Health; administered by local health departments. In its own words:
Every septic tank shall have a minimum capacity below the water line as specified in Table III ... 2 or less | 750; 3 | 1,000; 4 | 1,250; 5 | 1,500; 5 + | 1,500 plus 300 multiplied by the number of bedrooms over 5
Source: 410 IAC 6-8.3-60(c), Table III (Residential On-Site Sewage Systems), read 2026-10-20.
- Two bedrooms or fewer may use a 750-gallon tank; above five bedrooms each bedroom adds 300 gallons.
- A jetted tub over 125 gallons counts as an extra bedroom when sizing.
Indiana minimum tank size by bedrooms
| Bedrooms | Minimum tank | Versus the median state |
|---|---|---|
| 1 | 750 gal | −250 |
| 2 | 750 gal | — |
| 3 | 1,000 gal | same |
| 4 | 1,250 gal | +50 |
| 5 | 1,500 gal | same |
| 6 | 1,800 gal | — |
The first step up comes at 3 bedrooms, from 750 to 1,000 gallons, and a six-bedroom house needs 1,800 gallons. Beyond the table the rule adds 300 gallons for each extra bedroom. These are minimums: the permit can call for more, and a bigger tank needs pumping less often.
How Indiana compares with nearby states
Illinois requires 1,000 gallons for three bedrooms; Michigan sets no statewide figure; Ohio requires 1,500 gallons for three bedrooms. 37 of the 47 states listed here share Indiana's three-bedroom figure.
Before you size a tank in Indiana
- Bedrooms, not people, set the size in most rules. Rooms that could be used as bedrooms are usually counted, so check how your permitting office counts a den or a finished basement.
- Garbage disposals, grinder or ejector pumps and large tubs change the answer in many states; the points above list Indiana's adjustments.
- The tank is only half the system. The drainfield is sized separately from soil tests, and it is usually the bigger cost.
- A private well on the same lot has its own setbacks from the tank and field; the well pump and pressure tank calculators size the water side.
Figures are the state's minimum as written on 2026-10-20. Local health departments can require more; the permit issued for your property governs. See the methodology for how each state was read.