Septic Tank Size Calculator
Educational tank-size bands from bedrooms — not a health-department design. Click any i for detail.
House
Bedrooms
i
Bedrooms
Most codes size from bedrooms, not bathrooms. Count every legal bedroom. |
|
|---|---|
Extra gallons
i
Extra
Garbage disposal, high-flow fixtures, or a local bump. Leave 0 if none. |
How to use this calculator
- Enter bedroom count.
- Add extra gallons if your code or usage needs it.
- Read the planning size.
- Confirm with the health department and your installer.
Results explained
Common sketch: 1–2 bedrooms 750 gal, 3 bedrooms 1,000, 4 bedrooms 1,250, then +250 gal per extra bedroom. Install dollars sit on the septic tank installation cost page.
Quick reference: tank size
Many U.S. counties still talk in these bedroom bands — yours may not.
| Item | Detail |
|---|---|
| 1–2 bedrooms | 750 gal sketch |
| 3 bedrooms | 1,000 gal |
| 4 bedrooms | 1,250 gal |
| Each extra bedroom | +250 gal in this model |
Aerobic systems and shared fields are outside this sketch.
How the estimate is built
lookup(bedrooms) + extra gallons.
Example scenario
3 bedrooms → 1,000 gallons in this table.
FAQ
Bathrooms instead?
Codes usually key off bedrooms as occupancy.
Install cost?
Use the septic tank installation cost calculator.
Is 1,000 gal enough?
Only if the local code and soil say so.