Septic tank size by state / Pacific
Hawaii septic tank size
In Hawaii 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 Haw. Code R. §11-62-33.1(a)(4)-(5) (Hawaii Administrative Rules ch. 11-62). That matches the 1,000-gallon median of the 47 states listed here.
What the Hawaii rule says
The rule is Haw. Code R. §11-62-33.1(a)(4)-(5) (Hawaii Administrative Rules ch. 11-62), administered by Hawaii Department of Health, Wastewater Branch. In its own words:
The following schedule shall apply to septic tank sizing: No. of Bedrooms | Minimum Capacity (Gallons): 4 or less | 1000; 5 | 1250. ... Minimum capacity gallons = 1,000 + (Q-800)x 1.25, where Q=design flow
Source: Haw. Code R. §11-62-33.1(a)(4)-(5) (Hawaii Administrative Rules ch. 11-62), read 2026-10-20.
- One individual system may serve at most five bedrooms, so five is the top of the single-home table.
- A revision of the state wastewater rules (HAR 11-62) is in progress; check with the Department of Health before you build.
Hawaii 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 | 1,250 gal | −250 |
| 6 | See note | — |
One individual system may serve at most five bedrooms.
The first step up comes at 5 bedrooms, from 1,000 to 1,250 gallons. These are minimums: the permit can call for more, and a bigger tank needs pumping less often.
How Hawaii compares with nearby states
Alaska requires 1,000 gallons for three bedrooms; California sets no statewide figure; Oregon requires 1,000 gallons for three bedrooms; Washington requires 1,000 gallons for three bedrooms. 37 of the 47 states listed here share Hawaii's three-bedroom figure.
Before you size a tank in Hawaii
- 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 Hawaii'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.