Septic tank size by state / East South Central
Tennessee septic tank size
In Tennessee the minimum septic tank for a three-bedroom house is 900 gallons, rising to 1,000 gallons at four bedrooms. The figure comes from Tenn. Comp. R. & Regs. 0400-48-01-.08(1). That is 100 gallons less than the 1,000-gallon median of the 47 states listed here.
What the Tennessee rule says
The rule is Tenn. Comp. R. & Regs. 0400-48-01-.08(1), administered by Tennessee Department of Environment and Conservation (TDEC), Division of Water Resources. In its own words:
Number of Bedrooms / Septic Tank Capacity: 2 or less - 750 gallons; 3 - 900 gallons; 4(a) - 1000 gallons. (a) For each additional bedroom, add two hundred fifty (250) gallons
Source: Tenn. Comp. R. & Regs. 0400-48-01-.08(1), read 2026-10-20.
- Tennessee's three-bedroom minimum is 900 gallons; one and two bedrooms 750.
Tennessee minimum tank size by bedrooms
| Bedrooms | Minimum tank | Versus the median state |
|---|---|---|
| 1 | 750 gal | −250 |
| 2 | 750 gal | — |
| 3 | 900 gal | −100 |
| 4 | 1,000 gal | −200 |
| 5 | 1,250 gal | −250 |
| 6 | 1,500 gal | — |
The first step up comes at 3 bedrooms, from 750 to 900 gallons, and a six-bedroom house needs 1,500 gallons. Beyond the table the rule adds 250 gallons for each extra bedroom. These are minimums: the permit can call for more, and a bigger tank needs pumping less often.
How Tennessee compares with nearby states
Alabama requires 1,000 gallons for three bedrooms; Kentucky requires 1,000 gallons for three bedrooms; Mississippi requires 900 gallons for three bedrooms. 4 of the 47 states listed here share Tennessee's three-bedroom figure.
Before you size a tank in Tennessee
- 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 Tennessee'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.