Septic tank size by state / Mid-Atlantic
Pennsylvania septic tank size
In Pennsylvania the minimum septic tank for a three-bedroom house is 900 gallons, rising to 1,250 gallons at four bedrooms. The figure comes from 25 Pa. Code § 73.31(a), which sizes the tank from design flow; the bedroom figures below are that rule's arithmetic. That is 100 gallons less than the 1,000-gallon median of the 47 states listed here.
What the Pennsylvania rule says
The rule is 25 Pa. Code § 73.31(a), administered by Pennsylvania Department of Environmental Protection (DEP); permits issued by local agencies (SEOs). In its own words:
The minimum liquid septic tank capacity for any installation is 900 gallons. ... For single-family dwelling units, not served by a community onlot system, a minimum daily flow of 400 gpd shall be used ... This figure shall be increased by 100 gallons for each additional bedroom over three. ... 0-500 gpd: (3.5 x flow exceeding 400 gpd) + (900); 500-5,000: (1.50 x flow exceeding 500 gpd) + (1,250)
Source: 25 Pa. Code § 73.31(a), read 2026-10-20.
- Pennsylvania's rule is a formula on daily flow; the bedroom figures here are that arithmetic.
- The flow allowance already includes garbage grinders, washers, dishwashers and water softeners.
Pennsylvania minimum tank size by bedrooms
| Bedrooms | Minimum tank | Versus the median state |
|---|---|---|
| 1 | 900 gal | −100 |
| 2 | 900 gal | — |
| 3 | 900 gal | −100 |
| 4 | 1,250 gal | +50 |
| 5 | 1,400 gal | −100 |
| 6 | 1,550 gal | — |
The first step up comes at 4 bedrooms, from 900 to 1,250 gallons, and a six-bedroom house needs 1,550 gallons. These are minimums: the permit can call for more, and a bigger tank needs pumping less often.
How Pennsylvania compares with nearby states
New Jersey requires 1,000 gallons for three bedrooms; New York requires 1,000 gallons for three bedrooms. 4 of the 47 states listed here share Pennsylvania's three-bedroom figure.
Before you size a tank in Pennsylvania
- Bedrooms, not people, set the size in most rules. Rooms that could be used as bedrooms are usually counted, so check how your permitting office counts a den or a finished basement.
- Garbage disposals, grinder or ejector pumps and large tubs change the answer in many states; the points above list Pennsylvania's adjustments.
- The tank is only half the system. The drainfield is sized separately from soil tests, and it is usually the bigger cost.
- A private well on the same lot has its own setbacks from the tank and field; the well pump and pressure tank calculators size the water side.
Figures are the state's minimum as written on 2026-10-20. Local health departments can require more; the permit issued for your property governs. See the methodology for how each state was read.