Septic tank size by state

Counts cover single-family homes. The 3-bedroom counts include Arizona, Florida and Texas, whose figure depends on the house (the table shows the conditions), and California and Kansas, whose figure is a state default that county programs replace.

Gallons of liquid capacity. Sort by any bedroom column; select a state for its full card and the rule text. Italic figures are calculated from the rule’s formula or per-bedroom step; upright ones are printed in the rule. Where a range is shown, the rule gives two figures — Texas without and with water-saving devices, Arizona for up to and over 7 plumbing fixture units per bedroom.

Every state starts from the same idea — the tank has to hold at least a day or two of the home’s wastewater so solids can settle — but writes it down in one of three ways.

A bedroom table

Most states print a table: so many gallons up to a bedroom count, then a fixed step for each bedroom beyond it. The steps differ more than the starting points. Connecticut adds 125 gallons a bedroom above three, Wyoming 150 above four, and most others 250. Some tables cover bands instead: Minnesota and Montana jump from 1,000 to 1,500 gallons at four bedrooms and to 2,000 at six.

A flow formula

Delaware, Louisiana, Massachusetts, Nebraska, Pennsylvania and Vermont set a daily design flow per bedroom and size the tank as a multiple of it, often with a floor. Massachusetts’ 1,500-gallon floor is above what its formula gives for up to six bedrooms, so every home up to six bedrooms gets 1,500. Pennsylvania’s formula gives 900 gallons for up to three bedrooms and 1,250 for four — a 350-gallon step, not a flat per-bedroom figure. For these states each figure here is calculated from the formula and shows its arithmetic.

Something besides bedrooms

Texas sizes from a flow that depends on living area and water-saving devices, so a 3-bedroom house (living area under 2,500 sq ft) needs 1,000 gal without devices and 750 gal with them. Florida uses whichever of bedrooms or building area gives the larger flow. Arizona adds a count of plumbing fixture units, and from 3 bedrooms up a house with more than 7 per bedroom needs the next size.

Work out your own house in the tank size calculator→

A disposal sends food solids to the tank, and the model code adds 50% for one. The states don’t agree:

• Add 50%: Georgia, Minnesota, New Hampshire, New Jersey and Vermont.
• Another percentage: Maine (+30% is one listed option), South Dakota (+20%). Maine’s rule says disposals “should not be used” with disposal fields and lists more capacity as one of several measures if one is.
• Add 250 gallons: Connecticut, Kentucky, New York and Rhode Island.
• Their own figures: Illinois (own table (e.g. 3 br 1,500)), Kansas (3 x daily flow (e.g. 3 br 1,350)), Nebraska (next column of table 3).
• Already allowed for in the table or flow: California, Maryland, Missouri, North Dakota and Pennsylvania.
• No extra volume, other conditions: Arkansas (no increase (grinders not recommended)), Massachusetts (two-compartment tank; no extra volume).
• Not addressed: the other 28 states’ rules don’t mention a disposal in sizing the tank.

Where a rule is silent, a bigger tank still gives the solids more room and stretches the time between pump-outs; it just isn’t required.

A second compartment (or a second tank in series) keeps more solids out of the drain field. 18 states require one for every home: Arizona, California, Colorado, Connecticut, Delaware, Florida, Georgia, Iowa, Maryland, Nevada, New Mexico, North Carolina, Ohio, Pennsylvania, Rhode Island, Tennessee, Texas and Washington. 11 require it only in some cases — with a garbage disposal or ejector pump, above a tank size or flow, or on poor soil. The rest allow a single-compartment tank, though several set proportions if you use two, and 4 say nothing in the rule reviewed.

The state rule is a minimum; the permit usually comes from a county or district health department, and it has the final say. In 26 states the rule text lets local bodies set stricter requirements or run their own programs — each card flags it. Three cases stand out:

• Michigan has no statewide rule for single-family homes; each local health department’s sanitary code sets the size.
• California and Kansas: county programs replace the state figure where they exist (California’s approved Local Agency Management Programs, Kansas’s county sanitary codes). The figures shown are the state defaults.
• Wisconsin sets the design flow but has no minimum tank table; the tank is sized in the approved design.

Before you buy a tank or accept a quote, ask the office that issues the permit which figure it applies. If it differs from the one here, theirs governs.

Official regulation text only. Each state was researched from its administrative code, statute, or the state agency’s own rule or official guidance — no installer sites, tank sellers or summaries. The 50 records cite 145 sources and carry 421 passages of rule text, shown on each state’s card.

An independent second pass. Every value and quote was then re-checked against the live source on September 26, 2026. That pass corrected citations, compartment rules and dates, removed figures that were inferred rather than stated (such as absolute minimums read off the smallest table row, and a per-bedroom increment for Mississippi found only in unofficial copies), and flagged Ohio’s 6-bedroom wording as unresolved rather than choosing a reading. No bedroom figure changed.

Stated or calculated. 186 figures are printed in a rule; 100 are calculated from the rule’s own formula or per-bedroom step, and our build re-does each calculation and fails if it doesn’t reproduce the verified figure. Where a rule leaves rounding unstated (North Carolina, Texas at 6 bedrooms) we round up and say so.

Limits. Figures are minimum liquid capacity for a single-family home using a conventional septic tank; aerobic units, nitrogen-reducing systems and other alternatives follow their own approvals. Rules change, and local codes can add to them.

This is a research summary, not permit advice. The local health department issues the permit; confirm the minimum for your property with it before you buy a tank.

The full table — all 50 states, 1–6 bedroom figures with how each was obtained, the disposal and compartment rules, authority, regulation and every source URL — is free to reuse under CC BY 4.0: credit Septic Fixes with a link to this page.

Download the CSV (70 KB)

Linking to one state? Add ?state= and its two-letter code, such as ?state=TX, to this page or to the calculator.