Calculate Septic Tank Size
Gallons per person / day
Results
Recommended Tank Volume
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Suggested Tank Dimensions
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Assumes 2:1 length-to-width ratio and typical depth
Soakaway Area Needed
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Estimates only. Local codes vary—confirm with your municipality or engineer.
How this septic tank size calculator works
We estimate daily wastewater flow, multiply by retention time, and apply a safety factor. Minimum capacity is enforced for typical bedroom counts. Soakaway area is sized using soil absorption rates.
Sizing basics
Use this quick guide to understand what each input means and why it affects septic tank size.
- Region preset: sets typical daily water use for that country/region.
- Bedrooms vs occupants: bedrooms set minimum capacity; occupants set daily flow.
- Daily flow per person: higher usage increases tank volume.
- Retention days: longer retention increases required volume.
- Safety factor: adds a buffer for peak usage and future changes.
- Soil absorption: controls soakaway size based on soil drainage.
- Units: switch between meters/liters and feet/gallons instantly.
FAQ
What size septic tank do I need in the USA?
Typical homes use 1,000–1,500 gallons depending on bedrooms and local requirements. Use the calculator for a tailored estimate.
Does this follow U.S. codes?
This is a sizing estimator. Always confirm with state or county regulations.