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Calcimator

Septic Tank Sizing Calculator

Size septic tanks and drain fields based on bedrooms, occupants, soil percolation rate, and daily wastewater flow.

Inputs

EPA/state codes: 1–2 BR 750 gal min; 3 BR 1,000 gal; 4 BR 1,200 gal; 5–6 BR 1,500 gal min

min/inch

EPA 625/R-00/008: sandy 1–5 min/in; loam 5–30 min/in; clay loam 30–60 min/in; >120 min/in unsuitable

GPD

Results

Minimum Tank Size

1,000 gallons

≈ 25 bathtubs

Drain Field Area

500 sq ft

≈ 12 king-size beds

Trench Length (3ft wide)167 ft
Pumping Frequency1.4 years
How to Use This Calculator
  1. Enter the number of bedrooms — most codes size septic systems by bedroom count regardless of actual occupancy.
  2. Enter the actual number of occupants for a more accurate daily flow estimate.
  3. Input the soil percolation rate in minutes per inch from a perc test (slower soil = larger drain field).
  4. Review Minimum Tank Size in gallons and Drain Field Area in square feet from the results.
  5. Use Pumping Frequency to schedule routine service — most residential tanks need pumping every 3-5 years.
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