Septic Tank Size Calculator
Estimate septic tank size from household size and daily water use, with a clearly identified Minnesota sizing reference.
A clearer picture starts here.
Complete the details and calculate your plan. We’ll show the assumptions with your result.
Keep your installation permit and service records nearby if you have them.
How the Septic Tank Size Calculator works
Daily flow = household members × entered gallons per person per day. The editable 70-gallon default comes from EPA household water-use guidance. A two-day liquid-volume illustration multiplies flow by 2; this is our educational scenario, not an EPA sizing formula. Minnesota mode uses Rule 7080.1930 bedroom tiers and its 50% disposal/ejector adjustment once. Local design flow, soils, setbacks and approval are not calculated.
Planning guidance only. Local requirements and professional inspections take precedence.
Sources you can check
EPA — How to care for your septic system ↗
Maintenance and household water use · Checked 2026-10-04
Minnesota Rule 7080.1930 — Septic tank capacity ↗
Minnesota dwelling tank capacity; not a nationwide rule · Checked 2026-10-04