Septic tank size by state
The minimum septic tank for a single-family home, by bedrooms, as each state's own rule sets it. 49 states are listed; in the median one a three-bedroom house needs 1,000 gallons and a four-bedroom house 1,200. Each state page quotes the rule, links to it and lists the adjustments it makes for garbage disposals, pumps and large tubs.
| State | 1 BR | 3 BR | 4 BR | 5 BR | Rule |
|---|---|---|---|---|---|
| Alabama | 1,000 | 1,000 | 1,000 | 1,500 | Ala. Admin. Code r. 420-3-1-.17(5) and Table 9 (420-3-1-T9) |
| Alaska | 1,000 | 1,000 | 1,250 | 1,500 | 18 AAC 72.530(e)(2) (table) |
| Arizona | 1,000 | 1,000 | 1,250 | 1,500 | Ariz. Admin. Code R18-9-A314(4)(a) |
| Arkansas | 1,000 | 1,000 | 1,250 | 1,500 | Rules Pertaining to Onsite Wastewater Systems (2024,... |
| California | Set by county or local health department | Water Quality Control Policy for Siting, Design, Operation... | |||
| Colorado | 1,000 | 1,000 | 1,250 | 1,500 | 5 CCR 1002-43 (Regulation 43, On-site Wastewater Treatment... |
| Connecticut | 1,000 | 1,000 | 1,125 | 1,250 | Public Health Code §19-13-B103 |
| Delaware | 1,000 | 1,000 | 1,000 | 1,500 | 7 Del. Admin. Code 7101 §5.3.14.4 (septic tanks) and... |
| Florida | 900 | 900 | 1,050 | 1,200 | Fla. Admin. Code R. 62-6.008(1) Table I (design flow) and... |
| Georgia | 1,000 | 1,000 | 1,000 | 1,250 | Ga. Comp. R. & Regs. r. 511-3-1-.05(3) (Septic Tanks -... |
| Hawaii | 1,000 | 1,000 | 1,000 | 1,250 | Haw. Code R. §11-62-33.1(a)(4)-(5) (Hawaii Administrative... |
| Idaho | 1,000 | 1,000 | 1,000 | 1,250 | IDAPA 58.01.03.007.08.a (Individual/Subsurface Sewage... |
| Illinois | 750 | 1,000 | 1,250 | 1,500 | 77 Ill. Adm. Code 905.40(c) and Part 905 Appendix A,... |
| Indiana | 750 | 1,000 | 1,250 | 1,500 | 410 IAC 6-8.3-60(c), Table III (Residential On-Site Sewage... |
| Iowa | 1,250 | 1,250 | 1,500 | 1,750 | Iowa Admin. Code 567—69.3(2)(a), Table I (as renumbered by... |
| Kansas | 1,000 | 1,000 | 1,200 | 1,500 | K.A.R. 28-5-6 to 28-5-9 and KDHE Bulletin 4-2, 'Minimum... |
| Kentucky | 1,000 | 1,000 | 1,250 | 1,500 | 902 KAR 10:085 Section 6(2), Table 2 'Minimum Capacity of... |
| Louisiana | 500 | 1,000 | 1,250 | 1,500 | LAC 51:XIII.715(D) (Sanitary Code Part XIII, Sewage... |
| Maine | 750 | 1,000 | 1,000 | 1,250 | 10-144 CMR Ch. 241 (Subsurface Wastewater Disposal Rules),... |
| Maryland | 1,000 | 1,000 | 1,250 | 1,500 | COMAR 26.04.02.05D (Design and Construction of Conventional... |
| Massachusetts | 1,500 | 1,500 | 1,500 | 1,500 | 310 CMR 15.223(1) (Title 5, septic tank capacity) |
| Michigan | Set by county or local health department | No statewide residential code | |||
| Minnesota | 1,000 | 1,000 | 1,500 | 1,500 | Minn. R. 7080.1930 (Septic tank capacity), Table V |
| Mississippi | 750 | 900 | 1,200 | 1,500 | MSDH On-site Wastewater Regulations, Miss. Admin. Code Title... |
| Missouri | 1,000 | 1,000 | 1,250 | 1,500 | 19 CSR 20-3.060(4)(B)16 and Table 4 (Minimum Construction... |
| Montana | 1,000 | 1,000 | 1,500 | 1,500 | Circular DEQ-4 (December 2023 edition), Section 5.1.6.2... |
| Nebraska | 1,000 | 1,000 | 1,250 | 1,500 | Title 124 (Onsite Wastewater Treatment Systems, eff. June... |
| Nevada | 1,000 | 1,000 | 1,200 | 1,500 | NAC 444.8306 (Capacity of septic tank serving single-family... |
| New Hampshire | 1,250 | 1,250 | 1,250 | 1,500 | N.H. Code Admin. R. Env-Wq 1010.01 (septic tank sizing) |
| New Jersey | 1,000 | 1,000 | 1,000 | 1,250 | N.J.A.C. 7:9A-8.2(b)1 and (c) |
| New Mexico | 750 | 1,000 | 1,200 | 1,500 | 20.7.3.201(Q)(1) NMAC and Table 201.2 (Capacity of septic... |
| New York | 1,000 | 1,000 | 1,250 | 1,500 | 10 NYCRR Appendix 75-A.6 (Septic tanks and enhanced... |
| North Carolina | 1,000 | 1,000 | 1,000 | 1,250 | 15A NCAC 18E .0801 (Septic Tank Capacity Requirements),... |
| North Dakota | 1,000 | 1,000 | 1,200 | 1,500 | N.D. Admin. Code 62-03.1-03-07(1) (Septic tanks) |
| Ohio | 1,000 | 1,500 | 2,000 | 2,000 | OAC 3701-29-12(C)(1) |
| Oklahoma | 1,000 | 1,000 | 1,000 | 1,250 | OAC 252:641-7-4(a) |
| Oregon | 1,000 | 1,000 | 1,000 | 1,500 | OAR 340-071-0220(3)(a)(C) |
| Pennsylvania | 900 | 900 | 1,250 | 1,400 | 25 Pa. Code § 73.31(a) |
| Rhode Island | 1,000 | 1,000 | 1,250 | 1,500 | 250-RICR-150-10-6.27(B)(1) (septic tanks) |
| South Carolina | 1,000 | 1,000 | 1,000 | 1,250 | S.C. Code Regs. R.61-56 § 201.1(3) |
| South Dakota | 1,000 | 1,000 | 1,250 | 1,500 | ARSD 74:53:01:25(1) |
| Tennessee | 750 | 900 | 1,000 | 1,250 | Tenn. Comp. R. & Regs. 0400-48-01-.08(1) |
| Texas | 750 | 1,000 | 1,250 | 1,250 | 30 TAC §285.91(2) Table II (septic tank minimum liquid... |
| Utah | 1,000 | 1,000 | 1,250 | 1,500 | Utah Admin. Code R317-4-6(7)(b) |
| Vermont | 1,000 | 1,000 | 1,000 | 1,000 | Wastewater System and Potable Water Supply Rules (effective... |
| Virginia | 750 | 900 | 1,200 | 1,500 | 12VAC5-610-815 (Septic tank design), Table 5.2 |
| Washington | 1,000 | 1,000 | 1,000 | 1,250 | WAC 246-272A-0232(2)(a), Table VII |
| West Virginia | 1,000 | 1,000 | 1,000 | 1,250 | W. Va. Code R. § 64-47-6.4.a (64CSR47, Sewage Treatment and... |
| Wyoming | 1,000 | 1,000 | 1,000 | 1,150 | WDEQ Water Quality Rules Ch. 25, § 25-10(a)(iii)(A) (020-25... |
Gallons, minimum liquid capacity. Not yet listed because the state's table could not be read in full: Wisconsin. Sources and method: methodology.
What sets the size
Most states size the tank by bedrooms, because bedrooms are a stable stand-in for how many people a house can hold. A few size it from design flow — gallons per day per bedroom — and then multiply: Massachusetts requires twice the design flow, Louisiana two and a half times, Pennsylvania uses a formula on daily flow. California and Michigan leave the number to counties and local health departments.
The common pattern is 1,000 gallons for up to three bedrooms and 250 more for each bedroom after that, but the exceptions matter: New Hampshire starts at 1,250 for up to four bedrooms, Iowa at 1,250 for up to three, Ohio asks 1,500 at three bedrooms in two compartments, and Florida, Mississippi, Pennsylvania, Tennessee, Virginia allow 900 for three. Garbage disposals add 50% in Georgia, Minnesota, New Hampshire and New Jersey and count as an extra bedroom in New York.
For the water side of the same house, see well pump size by depth and pressure tank size by pump flow.