Septic tank size by state / West South Central
Texas septic tank size
In Texas 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 30 TAC §285.91(2) Table II (septic tank minimum liquid capacity) and §285.91(3) Table III (wastewater usage rate), which sizes the tank from design flow; the bedroom figures below are that rule's arithmetic. That matches the 1,000-gallon median of the 47 states listed here.
What the Texas rule says
The rule is 30 TAC §285.91(2) Table II (septic tank minimum liquid capacity) and §285.91(3) Table III (wastewater usage rate), administered by Texas Commission on Environmental Quality (TCEQ), On-Site Sewage Facilities (OSSF) program; local authorized agents. In its own words:
SEPTIC TANK MINIMUM LIQUID CAPACITY ... For Q equal to or less than 250 gal/day: V = 750 gallons ... For Q greater than or equal to 251 gal/day but less than or equal to 350 gal/day: V = 1000 gallons ... 351 ... to 500 gal/day: V = 1250 gallons ... 501 ... to 1000 gal/day: V = 2.5 Q
Source: 30 TAC §285.91(2) Table II (septic tank minimum liquid capacity) and §285.91(3) Table III (wastewater usage rate), read 2026-10-20.
- Texas sizes in two steps: daily flow from bedrooms and living area, then the tank from that flow.
- The figures here are for homes without water-saving fixtures; with them, three bedrooms need 750 gallons.
- If the house is larger than the floor-area limit for its bedroom count, use the next row.
Texas 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 | 1,250 gal | −250 |
| 6 | 1,313 gal | — |
The first step up comes at 3 bedrooms, from 750 to 1,000 gallons, and a six-bedroom house needs 1,313 gallons. These are minimums: the permit can call for more, and a bigger tank needs pumping less often.
How Texas compares with nearby states
Arkansas requires 1,000 gallons for three bedrooms; Louisiana requires 1,000 gallons for three bedrooms; Oklahoma requires 1,000 gallons for three bedrooms. 37 of the 47 states listed here share Texas's three-bedroom figure.
Before you size a tank in Texas
- 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 Texas'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.