Septic tank size by state / 4 bedrooms
47 state rules · 4-bedroom house
4-bedroom septic tank size by state
Across the 47 states whose rule prints a figure for a 4-bedroom house, the median minimum septic tank is 1,200 gallons. The smallest is 1,000 gallons (Alabama, Delaware, Georgia, Hawaii, Idaho, Maine, New Jersey, North Carolina, Oklahoma, Oregon, South Carolina, Tennessee, Vermont, Washington, West Virginia, Wyoming) and the largest 2,000 (Ohio), a spread of 1,000 gallons for the same house. 18 states set exactly 1,250 gallons, the most common figure.
- 1Median, 4 bedrooms 1,200 gal
- 2Largest, OH 2,000 gal
- 3States with a figure 47
Minimum tank for 4 bedrooms, grouped by size
States are grouped by the gallons their rule requires for a 4-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 |
|---|---|---|
| 1,000 gal | 16 | Alabama, Delaware*, Georgia, Hawaii, Idaho, Maine, New Jersey, North Carolina, Oklahoma, Oregon, South Carolina, Tennessee, Vermont*, Washington, West Virginia, Wyoming |
| 1,050 gal | 1 | Florida* |
| 1,125 gal | 1 | Connecticut |
| 1,200 gal | 6 | Kansas, Mississippi, Nevada, New Mexico, North Dakota, Virginia |
| 1,250 gal | 18 | Alaska, Arizona, Arkansas, Colorado, Illinois, Indiana, Kentucky, Louisiana*, Maryland, Missouri, Nebraska*, New Hampshire, New York, Pennsylvania*, Rhode Island, South Dakota, Texas*, Utah |
| 1,500 gal | 4 | Iowa, Massachusetts*, Minnesota, Montana |
| 2,000 gal | 1 | Ohio |
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 fourth bedroom adds
Going from 3 to 4 bedrooms raises the minimum in 30 of the 47 states and leaves it unchanged in 17. The biggest jump is in Minnesota, where the minimum goes from 1,000 to 1,500 gallons (+500). The median moves from 1,000 gallons at 3 bedrooms to 1,200 here. At 5 bedrooms it is 1,500.
23 states ask for more than the 1,200-gallon median and 18 for less. Most rules step up in fixed increments once a house passes a threshold, so whether the fourth bedroom changes the tank depends on where that state's threshold sits. Two houses with the same floor plan can need tanks 1,000 gallons apart on either side of a state line.
States with no 4-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.
Reading these numbers for a 4-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 5-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 · 5 bedrooms · 6 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.