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Septic tank size calculator

Your state sets the smallest septic tank a house may have. This tool shows that rule and the document it comes from.

Work out the tank size your state asks for

Three questions. The answer names the rule it rests on.

The smallest tank each state allows

One row per state, read off that state’s own code. A state joins this table the day we source its rule, and not before.

StateSmallest tankWhat the rule coversSource
Arizona 1,000 gallons a 3-bedroom house with 21 or fewer plumbing fixtures Arizona Administrative Code, Title 18, Chapter 9 — Department of Environmental Quality, Water Pollution Control · checked 2026-09-23
Arkansas 1,000 gallons a house with 1, 2 or 3 bedrooms Appendix C sets this floor for a house that size. Arkansas State Board of Health, Rules Pertaining to Onsite Wastewater Systems, promulgated under Ark. Code Ann. § 14-236-101 et seq. · checked 2026-09-23
Connecticut 1,000 gallons a house with 1 to 3 bedrooms Regulations of Connecticut State Agencies §§ 19-13-B100a and 19-13-B103, effective September 1, 2026 · checked 2026-09-23
Delaware 1,000 gallons a dwelling with four bedrooms or fewer This rule is in § 5.3.14.4. The tank must have two compartments. The larger one holds most of the liquid. Delaware Administrative Code, Title 7, § 7101 · checked 2026-09-23
Florida 900 gallons a 3-bedroom house Rule 62-6.008(2) sets the minimum by the home's daily flow. Florida Administrative Code, Chapter 62-6 · checked 2026-09-23
Hawaii 1,000 gallons a house of four bedrooms or fewer Hawaii Administrative Rules, Title 11, Chapter 62 · checked 2026-09-23
Louisiana 500 gallons any home, as the statewide floor A bigger home needs a bigger tank, sized to its daily flow. Louisiana Administrative Code, Title 51, Part XIII, §715 — Septic Tanks · checked 2026-09-23
New Hampshire 1,250 gallons a house or senior home with four bedrooms or fewer A bigger home needs a bigger tank under the same rule. New Hampshire Code of Administrative Rules, Chapter Env-Wq 1000 · checked 2026-09-23
New Mexico 1,000 gallons a home with two or three bedrooms A one-bedroom home needs a smaller tank. A bigger home needs a bigger one. New Mexico Administrative Code, Title 20, Chapter 7, Part 3 · checked 2026-09-23
North Carolina 1,000 gallons a dwelling unit with four bedrooms or fewer (15A NCAC 18E .0801, Table XIV) A two compartment tank, or two tanks in series, meets the rule. N.C. Administrative Code, Title 15A, Subchapter 18E · checked 2026-09-23
Texas 1,000 gallons a 3-bedroom house Texas Administrative Code, Title 30, Chapter 285 · checked 2026-09-23
Vermont 1,000 gallons a wastewater system with a design flow of 560 gallons a day or less A design flow above that limit needs a tank sized at twice the flow. See Table 9-1. Vermont Environmental Protection Rules, Chapter 1 · checked 2026-09-23
Washington 1,000 gallons a house with four bedrooms or fewer See Table VII for homes with more than four bedrooms. Washington Administrative Code § 246-272A-0232 · checked 2026-09-23

Sources

Every figure on this page has a government source and the date we checked it.

  1. Arizona Administrative Code, Title 18, Chapter 9 — Department of Environmental Quality, Water Pollution Control · checked 2026-09-23
  2. Arkansas State Board of Health, Rules Pertaining to Onsite Wastewater Systems, promulgated under Ark. Code Ann. § 14-236-101 et seq. · checked 2026-09-23
  3. Regulations of Connecticut State Agencies §§ 19-13-B100a and 19-13-B103, effective September 1, 2026 · checked 2026-09-23
  4. Delaware Administrative Code, Title 7, § 7101 · checked 2026-09-23
  5. Florida Administrative Code, Chapter 62-6 · checked 2026-09-23
  6. Hawaii Administrative Rules, Title 11, Chapter 62 · checked 2026-09-23
  7. Louisiana Administrative Code, Title 51, Part XIII, §715 — Septic Tanks · checked 2026-09-23
  8. New Hampshire Code of Administrative Rules, Chapter Env-Wq 1000 · checked 2026-09-23
  9. New Mexico Administrative Code, Title 20, Chapter 7, Part 3 · checked 2026-09-23
  10. N.C. Administrative Code, Title 15A, Subchapter 18E · checked 2026-09-23
  11. Texas Administrative Code, Title 30, Chapter 285 · checked 2026-09-23
  12. Vermont Environmental Protection Rules, Chapter 1 · checked 2026-09-23
  13. Washington Administrative Code § 246-272A-0232 · checked 2026-09-23

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