Septic tank size by state / New England
Maine septic tank size
In Maine the minimum septic tank for a three-bedroom house is 1,000 gallons, and four bedrooms need the same 1,000 gallons. The figure comes from 10-144 CMR Ch. 241 (Subsurface Wastewater Disposal Rules), Section 7(G) and Table 7A. That matches the 1,000-gallon median of the 47 states listed here.
What the Maine rule says
The rule is 10-144 CMR Ch. 241 (Subsurface Wastewater Disposal Rules), Section 7(G) and Table 7A; design flows Table 5A, administered by Maine Department of Health and Human Services, Maine CDC, Division of Environmental and Community Health (Subsurface Wastewater Program). In its own words:
"The minimum liquid capacity of the septic tank(s) serving 1 to 3-family dwelling units must meet the capacity requirements of Table 7A for each dwelling unit." Table 7A: 1 Bedroom 750 gallons; 2 Bedrooms 750 gallons; 3 Bedrooms 1,000 gallons; 4 Bedrooms 1,000 gallons; 5 Bedrooms 1,250 gallons or; For each additional 250 gallons per bedroom. 7(G)(3): "The minimum liquid capacity of an individual septic tank must be 750 gallons for any use."
Source: 10-144 CMR Ch. 241 (Subsurface Wastewater Disposal Rules), Section 7(G) and Table 7A, read 2026-10-20.
- One and two-bedroom homes may use 750 gallons; three and four bedrooms 1,000 gallons.
- Capacity is per dwelling unit, so a duplex adds the two units' sizes.
Maine minimum tank size by bedrooms
| Bedrooms | Minimum tank | Versus the median state |
|---|---|---|
| 1 | 750 gal | −250 |
| 2 | 750 gal | — |
| 3 | 1,000 gal | same |
| 4 | 1,000 gal | −200 |
| 5 | 1,250 gal | −250 |
| 6 | 1,500 gal | — |
The first step up comes at 3 bedrooms, from 750 to 1,000 gallons, and a six-bedroom house needs 1,500 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 Maine compares with nearby states
Connecticut requires 1,000 gallons for three bedrooms; Massachusetts requires 1,500 gallons for three bedrooms; New Hampshire requires 1,250 gallons for three bedrooms; Rhode Island requires 1,000 gallons for three bedrooms; Vermont requires 1,000 gallons for three bedrooms. 37 of the 47 states listed here share Maine's three-bedroom figure.
Before you size a tank in Maine
- 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 Maine'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.