Texas septic tank size: bedrooms, square feet and gallons
Texas A&M AgriLife Extension lists a 1,000-gallon minimum septic tank for a three-bedroom house under 2,500 square feet. State Table II sizes the tank from daily wastewater flow in Table III; a flow of 251 to 350 gallons a day needs at least 1,000 gallons. Local rules can require more. [1] [2] [6]
Last checked · sources below · about this page
Not legal advice. These are state minimums used for planning. Your permitting authority and the licensed designer set the size for your lot.
Minimum tank size by bedrooms and house size
- AgriLife's planning table
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Texas A&M AgriLife Extension publishes minimum septic tank capacities for residential houses by bedroom count and house size. A three-bedroom house under 2,500 square feet uses a 1,000-gallon tank. [1]
| Bedrooms | House size (square feet) | Tank capacity (gallons) |
|---|---|---|
| 1 or 2 | less than 1,500 | 750 |
| 3 | less than 2,500 | 1,000 |
| 4 | less than 3,500 | 1,250 |
| 5 | less than 4,500 | 1,250 |
| 6 | less than 5,500 | 1,315 |
Note: AgriLife's Table 1. Designers size from wastewater flow under the state tables; local rules can require a larger tank.
How the state tables size a tank
Under Table II of 30 TAC §285.91, a home with a daily flow of 251 to 350 gallons needs at least a 1,000-gallon septic tank. The state septic rules put tank sizing in Table II of section 285.91. The designer first picks a daily wastewater usage rate (Q) from Table III, then applies the Table II formulas.
- Table II minimum liquid capacity
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The official table is 30 TAC §285.91(2). For a daily flow (Q) of 250 gallons or less, the minimum tank is 750 gallons. For Q of 251 to 350 gallons a day, 1,000 gallons. For Q of 351 to 500 gallons a day, 1,250 gallons. For Q of 501 to 1,000 gallons a day, volume is 2.5 × Q. For Q of 1,001 gallons a day or more, volume is 1,750 + 0.75 × Q. Your local permitting authority can require more. [2] [6]
- Wastewater usage rate (Table III)
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Table III in section 285.91 sets planning flows for dwellings by bedrooms and square footage, with and without water-saving devices. The designer may use accurate water-use records instead when the permitting authority accepts them, and must design for the higher flow when records exceed the table. [2]
- Example
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AgriLife's example: a three-bedroom house with a 1,000-gallon tank serving four people should be pumped about every 2.6 years on TCEQ's pumping table; the same tank serving two people is about every 5.9 years. [1] [3]
See also: TCEQ's pumping table
Aerobic treatment unit sizing
Under Table II of 30 TAC §285.91, a three-bedroom home under 2,501 square feet needs an aerobic unit rated for at least 360 gallons a day.
- Table II aerobic capacities
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Table II also sizes aerobic treatment units for residences by bedrooms and living area. Examples: three bedrooms and under 2,501 square feet need at least 360 gallons per day of treatment capacity; four bedrooms and under 3,501 square feet need 480; five bedrooms and under 4,501 square feet need 600. Your local permitting authority can require more. [2] [6]
See also: How the two types differ
Finding your tank size
About this page
Minimum septic tank sizes for Texas homes by bedroom count and house size, from Texas A&M AgriLife Extension, plus how TCEQ's Table II turns wastewater flow into tank gallons and where to find the size on your permit.
- Content last changed
- Last verified
- Sources
- 6 sources, all primary, listed below
- Not covered
- Exact design for a specific lot (that needs a licensed designer and a site evaluation); Commercial and restaurant flows; Pumping prices
Contacts
Your local septic permitting authority
- What they handle
- Keeps the permit and plans that show tank size. Find it by county with TCEQ's OARS lookup.
Sources
Each fact above cites one or more of these by number. Accessed is the date the source was last re-read.
- [1] Onsite wastewater treatment systems: Septic tank/soil absorption field (L-5227). Texas A&M AgriLife Extension. Primary source.
Supports: Bedroom and square-footage capacity table; 1,000-gallon three-bedroom example; 2.6 and 5.9-year pumping examples.
Publisher's date: Fact sheet dated Sep 2008.
Accessed: . - [2] OSSF Technical Information Packet (reprints 30 TAC §285.91(2) Table II and §285.91(3) Table III). Bandera County (TCEQ authorized agent). Primary source.
Supports: County reprint of Table II septic tank formulas and aerobic capacities, and Table III usage-rate notes.
Publisher's date: Undated county packet; official table is 30 TAC §285.91(2).
Accessed: . - [3] Advice for an Owner of an On-Site Sewage Facility (Septic System). Texas Commission on Environmental Quality (TCEQ). Primary source.
Supports: Pumping interval table used in the AgriLife example.
Publisher's date: Page last modified .
Accessed: . - [4] 30 Tex. Admin. Code § 285.3, General Requirements. Texas Administrative Code, via Cornell Legal Information Institute. Primary source.
Supports: Permit and plans on file.
Accessed: . - [5] OARS: Find a Local Contact (septic permitting authority by county). Texas Commission on Environmental Quality (TCEQ). Primary source.
Supports: Finding the local permitting authority.
Accessed: . - [6] 30 Tex. Admin. Code § 285.10, Delegation to Authorized Agents. Texas Administrative Code, via Cornell Legal Information Institute. Primary source.
Supports: Local permitting authorities may adopt standards more stringent than the state rules.
Accessed: .
Page history
- : Added that local permitting authorities can require larger tanks and treatment units than the state minimums. Re-checked every source.
- : First version of this page.