Septic tank size by state / Mountain
Utah septic tank size
In Utah 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 Utah Admin. Code R317-4-6(7)(b). That matches the 1,000-gallon median of the 47 states listed here.
What the Utah rule says
The rule is Utah Admin. Code R317-4-6(7)(b); design flow R317-4-6(4)(a), administered by Utah Department of Environmental Quality, Division of Water Quality; local health departments. In its own words:
1,000 gallons for up to three bedroom homes ... 1,250 gallons for four bedroom homes ... Two hundred fifty gallons per bedroom shall be added to the liquid capacity of the tank ... Unfinished basements shall be counted as a minimum of one additional bedroom.
Source: Utah Admin. Code R317-4-6(7)(b), read 2026-10-20.
- An unfinished basement counts as at least one extra bedroom, so a three-bedroom home with one is sized as four (1,250 gallons).
Utah 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 Utah compares with nearby states
Arizona requires 1,000 gallons for three bedrooms; Colorado requires 1,000 gallons for three bedrooms; Idaho requires 1,000 gallons for three bedrooms; Montana requires 1,000 gallons for three bedrooms; Nevada requires 1,000 gallons for three bedrooms; New Mexico requires 1,000 gallons for three bedrooms; Wyoming requires 1,000 gallons for three bedrooms. 37 of the 47 states listed here share Utah's three-bedroom figure.
Before you size a tank in Utah
- 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 Utah'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.