Free Tool
Septic Tank Size Calculator
An undersized septic tank leads to frequent pumping, slow drains, and costly system failures. Most states set minimum tank sizes based on bedroom count, but actual household water usage often demands more capacity. Use this calculator to determine the right tank size before you call an installer.
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Standard Septic Tank Sizes by Bedroom Count
| Bedrooms | Minimum Tank Size | Daily Flow (est.) |
|---|---|---|
| 1-2 | 1,000 gal | 500 gpd |
| 3 | 1,000 gal | 750 gpd |
| 4 | 1,250 gal | 1,000 gpd |
| 5 | 1,500 gal | 1,250 gpd |
| 6+ | 1,750 gal | 1,500 gpd |
Source: EPA Design Manual for Onsite Wastewater Treatment and Disposal Systems. Actual requirements vary by jurisdiction.