Septic tank size by state / South Atlantic
Maryland septic tank size
In Maryland the minimum septic tank for a three-bedroom house is 1,000 gallons, rising to 1,250 gallons at four bedrooms. The figure comes from COMAR 26.04.02.05D (Design and Construction of Conventional On-Site Sewage Disposal Systems — Residential Septic Tank Size Criteria). That matches the 1,000-gallon median of the 47 states listed here.
What the Maryland rule says
The rule is COMAR 26.04.02.05D (Design and Construction of Conventional On-Site Sewage Disposal Systems — Residential Septic Tank Size Criteria), administered by Maryland Department of the Environment (administered by county health departments). In its own words:
Table: "3 or less" 1,000 gallon; "4" 1,250 gallons; "For each additional bedroom, add 250 gallons." "This table provides for use of garbage disposal units, automatic clothes washers, and other household appliances." §.05I: "For residential property the minimum design flow is based on 150 gpd per bedroom."
Source: COMAR 26.04.02.05D (Design and Construction of Conventional On-Site Sewage Disposal Systems — Residential Septic Tank Size Criteria), read 2026-10-20.
- The table applies to tanks that do not need a nitrogen-removing Best Available Technology (BAT) unit; many new Maryland systems do.
- County health departments issue permits and may be stricter.
Maryland minimum tank size by bedrooms
| Bedrooms | Minimum tank | Versus the median state |
|---|---|---|
| 1 | 1,000 gal | same |
| 2 | 1,000 gal | — |
| 3 | 1,000 gal | same |
| 4 | 1,250 gal | +50 |
| 5 | 1,500 gal | same |
| 6 | 1,750 gal | — |
The first step up comes at 4 bedrooms, from 1,000 to 1,250 gallons, and a six-bedroom house needs 1,750 gallons. Beyond the table the rule adds 250 gallons for each extra bedroom. These are minimums: the permit can call for more, and a bigger tank needs pumping less often.
How Maryland compares with nearby states
Delaware requires 1,000 gallons for three bedrooms; Florida requires 900 gallons for three bedrooms; Georgia requires 1,000 gallons for three bedrooms; North Carolina requires 1,000 gallons for three bedrooms; South Carolina requires 1,000 gallons for three bedrooms; Virginia requires 900 gallons for three bedrooms; West Virginia requires 1,000 gallons for three bedrooms. 37 of the 47 states listed here share Maryland's three-bedroom figure.
Before you size a tank in Maryland
- 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 Maryland'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.