Septic tank size by state / New England
Vermont septic tank size
In Vermont 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 Wastewater System and Potable Water Supply Rules (effective April 12, 2019), § 1-908 Table 9-1, which sizes the tank from design flow; the bedroom figures below are that rule's arithmetic. That matches the 1,000-gallon median of the 47 states listed here.
What the Vermont rule says
The rule is Wastewater System and Potable Water Supply Rules (effective April 12, 2019), § 1-908 Table 9-1; design flow § 1-803(c)–(d), administered by Vermont Department of Environmental Conservation, Drinking Water and Groundwater Protection Division. In its own words:
Table 9-1, Minimum Capacities for Septic Tanks: design flow 560 gallons per day or less, 1000 gallons; greater than 560 – less than 6500, 2 times design flow. § 1-803(d)(1): "The design flow of 70 gallons per day per person", with "the first 3 bedrooms in a living unit contain a minimum occupancy of 2 persons per bedroom" and "each additional bedroom beyond 3 contains a minimum occupancy of 1 person per bedroom."
Source: Wastewater System and Potable Water Supply Rules (effective April 12, 2019), § 1-908 Table 9-1, read 2026-10-20.
- Vermont sizes from design flow: 70 gallons a day per person, two people per bedroom for the first three bedrooms and one per bedroom after that, and at least two bedrooms.
- Any home up to 560 gallons a day of design flow — five bedrooms — needs 1,000 gallons; above that the tank is twice the design flow.
- A garbage disposal adds at least 50%, and a pump inside the tank or a pump station feeding it means a larger tank.
Vermont 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 | 1,000 gal | −200 |
| 5 | 1,000 gal | −500 |
| 6 | 1,260 gal | — |
The first step up comes at 6 bedrooms, from 1,000 to 1,260 gallons, and a six-bedroom house needs 1,260 gallons. These are minimums: the permit can call for more, and a bigger tank needs pumping less often.
How Vermont compares with nearby states
Connecticut requires 1,000 gallons for three bedrooms; Maine 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. 37 of the 47 states listed here share Vermont's three-bedroom figure.
Before you size a tank in Vermont
- 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 Vermont'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.