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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

Drain Field Area

500 sq ft

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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