Septic tank size by state / West North Central
Missouri septic tank size
In Missouri 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 19 CSR 20-3.060(4)(B)16 and Table 4 (Minimum Construction Standards for On-Site Sewage Disposal Systems). That matches the 1,000-gallon median of the 47 states listed here.
What the Missouri rule says
The rule is 19 CSR 20-3.060(4)(B)16 and Table 4 (Minimum Construction Standards for On-Site Sewage Disposal Systems), administered by Missouri Department of Health and Senior Services (DHSS), Division of Community and Public Health. In its own words:
(4)(B)16: "The liquid capacity of a septic tank serving a dwelling shall be based upon the number of bedrooms contemplated in the dwelling served and shall be at least as large as the capacities given in Table 4." Table 4: 1-3 1000; 4 1250; 5 1500. "For six (6) or more bedrooms, the septic tank shall be sized on the basis similar to an establishment." (4)(B)17: "V = 1.5Q + 500"
Source: 19 CSR 20-3.060(4)(B)16 and Table 4 (Minimum Construction Standards for On-Site Sewage Disposal Systems), read 2026-10-20.
- The table already allows for garbage grinders, washers and other appliances; no extra increase.
- Six or more bedrooms are sized by formula from design daily flow (120 gallons a day per bedroom).
Missouri 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 | See note | — |
Six or more bedrooms are sized by formula from design daily flow (V = 1.5Q + 500).
The first step up comes at 4 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 Missouri compares with nearby states
Iowa requires 1,250 gallons for three bedrooms; Kansas requires 1,000 gallons for three bedrooms; Minnesota requires 1,000 gallons for three bedrooms; Nebraska requires 1,000 gallons for three bedrooms; North Dakota requires 1,000 gallons for three bedrooms; South Dakota requires 1,000 gallons for three bedrooms. 37 of the 47 states listed here share Missouri's three-bedroom figure.
Before you size a tank in Missouri
- 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 Missouri'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.