Septic tank size by state / 6 bedrooms
42 state rules · 6-bedroom house
6-bedroom septic tank size by state
Across the 42 states whose rule prints a figure for a 6-bedroom house, the median minimum septic tank is 1,650 gallons. The smallest is 1,260 gallons (Vermont) and the largest 2,000 (Arizona, Iowa, Minnesota, Montana), a spread of 740 gallons for the same house. 15 states set exactly 1,500 gallons, the most common figure.
- 1Median, 6 bedrooms 1,650 gal
- 2Largest, AZ, IA, MN, MT 2,000 gal
- 3States with a figure 42
Minimum tank for 6 bedrooms, grouped by size
States are grouped by the gallons their rule requires for a 6-bedroom single-family house, smallest first. Each state name links to its page with the rule quoted, the full one-to-six-bedroom table and the adjustments for garbage disposals, pumps and large tubs.
| Minimum | States | Which states |
|---|---|---|
| 1,260 gal | 1 | Vermont* |
| 1,300 gal | 1 | Wyoming |
| 1,313 gal | 1 | Texas* |
| 1,350 gal | 1 | Florida* |
| 1,375 gal | 1 | Connecticut |
| 1,500 gal | 15 | Delaware*, Georgia, Idaho, Maine, Massachusetts*, Nevada, New Jersey, New Mexico, North Dakota, Oklahoma, Oregon, South Carolina, Tennessee, Washington, West Virginia |
| 1,550 gal | 1 | Pennsylvania* |
| 1,750 gal | 14 | Alabama, Alaska, Arkansas, Colorado, Illinois, Kentucky, Louisiana*, Maryland, Nebraska*, New Hampshire, New York, Rhode Island, South Dakota, Utah |
| 1,800 gal | 3 | Indiana, Kansas, Mississippi |
| 2,000 gal | 4 | Arizona, Iowa, Minnesota, Montana |
Gallons of minimum liquid capacity, from each state's own rule. * 8 states size the tank from design flow or a per-bedroom increment rather than a printed row; the figure is that rule's arithmetic, shown on the state page. Highlighted row: the median.
What the sixth bedroom adds
Going from 5 to 6 bedrooms raises the minimum in 36 of the 42 states and leaves it unchanged in 6. The biggest jump is in Arizona, where the minimum goes from 1,500 to 2,000 gallons (+500). The median moves from 1,500 gallons at 5 bedrooms to 1,650 here.
21 states ask for more than the 1,650-gallon median and 21 for less. Most rules step up in fixed increments once a house passes a threshold, so whether the sixth bedroom changes the tank depends on where that state's threshold sits. Two houses with the same floor plan can need tanks 740 gallons apart on either side of a state line.
States with no 6-bedroom figure here
- California sets no statewide tank volume; the county or local office that issues the permit decides.
- Michigan sets no statewide tank volume; the county or local office that issues the permit decides.
- Wisconsin sets no statewide tank volume; the county or local office that issues the permit decides.
- Hawaii: One individual system may serve at most five bedrooms.
- Missouri: Six or more bedrooms are sized by formula from design daily flow (V = 1.5Q + 500).
- North Carolina: Over five bedrooms the tank is sized from design daily flow (Table XV).
- Ohio: The rule's six-bedroom wording is ambiguous, so the six-bedroom size is not computed here.
- Virginia: Above 5 bedrooms the rule sizes the tank for 48 hours of design flow; the table stops at 5.
Reading these numbers for a 6-bedroom house
- These are minimums. The permit can require more, and a larger tank holds more solids between pumpings.
- Bedrooms are counted the way the permitting office counts them. A den, office or finished basement room that could be used for sleeping often counts, which can move a house into the 6-bedroom row.
- Adjustments change the answer. Several states add capacity for a garbage disposal, a basement sump or ejector pump ahead of the tank, or a large tub; the state pages list them.
- The tank is one part of the system. The drainfield is sized separately from soil tests. For the water side of the same house, see pressure tank size and well pump size by depth.
Other house sizes: 2 bedrooms · 3 bedrooms · 4 bedrooms · 5 bedrooms. How states size tanks is explained in the septic tank sizing guide; how each rule was read is on the methodology page.
Figures are each state's minimum as written on the date shown on its page (rules read 2026-10-20; Wisconsin 2026-10-21). Local health departments can require more; the permit issued for the property governs.