Calculate Septic Tank Size
Results
Suggested Tank Dimensions
Soakaway Area Needed
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. Switch units to get septic tank size in feet or meters instantly.
Sizing basics
This quick guide explains how the calculator works so you can trust the numbers and adjust inputs confidently.
- Region preset: sets a typical daily water use per person for that location; you can override it.
- Bedrooms: establishes a minimum tank size so small households still meet typical code baselines.
- Occupants: drives daily flow; more people = more wastewater = larger tank volume.
- Daily flow per person: includes bathing, cooking, laundry, and toilet use.
- Retention days: how long wastewater stays in the tank to let solids settle (usually 1.5–3 days).
- Safety factor: adds headroom for guests, seasonal usage, and future expansion.
- Soil absorption: used to size the soakaway/leach field; poor soils need larger area.
- Tank dimensions: estimated using a common 2:1 length-to-width ratio and typical depth.
- Unit toggle: switch between liters/meters and gallons/feet without losing your inputs.
Tip: If you know local code requirements, use the calculator as a starting point and then adjust to match those rules.
FAQ
What size septic tank do I need?
Most homes need 1,000–1,500 gallons (3,800–5,700 L), depending on occupants and local requirements. Use the calculator for a tailored estimate.
Is this septic tank size calculator accurate for my country?
It uses common design practices and region presets. Always verify with local codes (e.g., USA, UK, Australia, NZ, Philippines, India, Ontario).
Do I need a soakaway size calculator?
If your system includes a leach field or soakaway, yes. Soil type and percolation rate are critical for sizing.
What we do
We help homeowners and contractors estimate septic tank volume and soakaway size quickly.
Use the calculator to explore scenarios, then confirm with local regulations.
Systems and services
- Septic tank sizing
- Soakaway area estimates
- Retention time planning
- Safety factor guidance
- Unit conversion support
Find us
Serving homeowners and engineers across multiple regions.