Septic tank size by state / East South Central
Alabama septic tank size
In Alabama the minimum septic tank for a three-bedroom house is 1,000 gallons, and four bedrooms need the same 1,000 gallons. The figure comes from Ala. Admin. Code r. 420-3-1-.17(5) and Table 9 (420-3-1-T9). That matches the 1,000-gallon median of the 47 states listed here.
What the Alabama rule says
The rule is Ala. Admin. Code r. 420-3-1-.17(5) and Table 9 (420-3-1-T9), administered by Alabama Department of Public Health (State Committee of Public Health), Bureau of Environmental Services. In its own words:
Table 9, Septic Tank Capacities for Dwellings Without Advanced Treatment: 4 or fewer bedrooms, 1,000 gal; 5 bedrooms, 1,500 gal; each additional bedroom, add 250. "Capacities listed provide for a single system to serve household wastes from standard plumbing fixtures and appliances commonly used in a dwelling, including dishwasher, shower, bathtub, and automatic clothes washer."
Source: Ala. Admin. Code r. 420-3-1-.17(5) and Table 9 (420-3-1-T9), read 2026-10-20.
- Alabama keeps 1,000 gallons up to four bedrooms, then jumps to 1,500 at five.
- The table already allows for a dishwasher, shower, bathtub and clothes washer.
- The table applies to homes without advanced treatment.
Alabama minimum tank size by bedrooms
| Bedrooms | Minimum tank | Versus the median state |
|---|---|---|
| 1 | 1,000 gal | same |
| 2 | 1,000 gal | — |
| 3 | 1,000 gal | same |
| 4 | 1,000 gal | −200 |
| 5 | 1,500 gal | same |
| 6 | 1,750 gal | — |
The first step up comes at 5 bedrooms, from 1,000 to 1,500 gallons, and a six-bedroom house needs 1,750 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 Alabama compares with nearby states
Kentucky requires 1,000 gallons for three bedrooms; Mississippi requires 900 gallons for three bedrooms; Tennessee requires 900 gallons for three bedrooms. 37 of the 47 states listed here share Alabama's three-bedroom figure.
Before you size a tank in Alabama
- 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 Alabama'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.