Septic Tank Size for a 2-Bedroom House (state code tables)
The minimum septic tank for a 2-bedroom house is 900 to 1,000 gallons in the three states below, which publish fixed bedroom tables. Your county can require more.
Minimum tank by state
| State and rule | Minimum tank | Notes |
|---|---|---|
| Washington (WAC 246-272A-0232) | 1,000 gal | 240 gpd design flow; two compartments, first holds ½ to ⅔ |
| Pennsylvania (25 Pa. Code § 73.31) | 900 gal | 400 gpd design flow; 900 gal minimum for any home |
| Minnesota (Minn. R. 7080.1930) | 1,000 gal | 1,500 gal with a garbage disposal or sewage pump (+50%) |
What changes at 2 bedrooms
Two bedrooms is below every state's floor, so all three states require their minimum tank. Pennsylvania's 900 gallons is the smallest; Washington and Minnesota both start at 1,000. Pennsylvania also assumes 400 gallons a day for any home up to 3 bedrooms, so a small house is sized as if it had three. Washington's design flow is 240 gpd, which is the rule's minimum and equals 2 × 120.
Drain field for 2 bedrooms (Washington)
Washington sizes the drain field from design flow (240 gpd for 2 bedrooms) divided by the soil's loading rate in WAC 246-272A-0234 Table VIII. These are primary areas for ordinary septic tank effluent; a reserve area of the same size is also required. Try your own numbers in the drain field calculator.
| Washington soil type | Loading rate | Drain field area |
|---|---|---|
| Type 1 | 1.0 gal/sq ft/day | 240 sq ft |
| Type 2 | 1.0 gal/sq ft/day | 240 sq ft |
| Type 3 | 0.8 gal/sq ft/day | 300 sq ft |
| Type 4 | 0.6 gal/sq ft/day | 400 sq ft |
| Type 5 | 0.4 gal/sq ft/day | 600 sq ft |
| Type 6 | 0.2 gal/sq ft/day | 1,200 sq ft |
Before you buy a tank
Local health officers can require more than the state minimum; Washington's design-flow rule says so directly. Get the number from your local permit office or a licensed designer. Run other bedroom counts in the septic tank size calculator, or compare: 3 bedrooms · 4 bedrooms · 5 bedrooms.
Sources
- Washington Administrative Code 246-272A-0232, Septic tank sizing
- Washington Administrative Code 246-272A-0230, Design flow (120 gpd per bedroom, 240 gpd minimum)
- Washington Administrative Code 246-272A-0234, Soil dispersal components (Table VIII loading rates)
- 25 Pa. Code § 73.31, Standards for septic tanks
- Minnesota Rules 7080.1930, Septic tank capacity (Table V)