Septic Tank Size Calculator
Updated Formulas shown
Most codes size septic tanks by bedrooms. A typical 3-bedroom home needs at least a 1,000-gallon tank; add about 50% capacity if you run a garbage disposal.
Typical minimum septic tank
1,000 gal
- Design flow (150 gal/bedroom/day)
- 450 gal/day
- Common next size up
- 1,250 gal
Typical code minimums — many states require 1,000 gal for up to 3 bedrooms. Your county health department sets the actual requirement.
Quick reference
| Bedrooms | Tank | Design flow |
|---|---|---|
| 1 | 1000 gal | 150 gal/day |
| 2 | 1000 gal | 300 gal/day |
| 3 | 1000 gal | 450 gal/day |
| 4 | 1250 gal | 600 gal/day |
| 5 | 1500 gal | 750 gal/day |
| 6 | 1750 gal | 900 gal/day |
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Frequently asked questions
How often should a septic tank be pumped?
Every 3–5 years for a typical household; more often with a garbage disposal or more occupants.
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Estimates only. Check quantities with your supplier or contractor before ordering.