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Septic Tank & Drain Field Sizing Calculator

Size septic tanks, absorption fields, and pump chambers based on bedroom count, soil percolation, and local health codes

Source-aware septic planning screen for organizing preliminary onsite wastewater questions. Enter bedroom, flow, soil/perc, water-table, bedrock, trench, and system-type prompts to review local tank, drainfield, pump-chamber, mound, ATU, reserve-area, setback, and cost rows. The output is not a permit design, public-health approval, installer instruction, soil report, product certification, or substitute for state/county health-department and qualified designer review.

Pro Tip: Treat every perc, tank, absorption, setback, ATU, mound, and cost row as a prompt for source review. Local rules, site soil morphology, seasonal water table, bedrock, slope, well and surface-water setbacks, product listings, maintenance contracts, inspections, and AHJ requirements control actual suitability.

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Septic Tank & Drain Field Sizing Calculator
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How It Works

  1. Enter Dwelling Flow Prompts

    Enter bedroom count or a manual daily-flow prompt. Replace local 150 GPD/bedroom and garbage-disposal assumptions with the current local design-flow rule, dwelling plan, fixture use, water-use records, and permit basis.

  2. Enter Site Evaluation Prompts

    Select a soil/perc prompt and enter water-table, bedrock, and trench-width prompts. Actual suitability requires site-specific soil morphology, perc testing, seasonal high-water evidence, slope, floodplain, and replacement-area review.

  3. Select System Type Prompt

    Choose conventional, pressure, mound, or ATU prompts only to expose source gaps. Product listings, NSF/ANSI or local approval, dose controls, maintenance contracts, inspections, and local rules control final system selection.

  4. Review Local Sizing Rows

    Review tank, absorption area, trench length, pump chamber, mound fill, reserve area, and cost prompts. Treat high-water, bedrock, fast/slow perc, disposal, and ATU flags as reasons for qualified review.

  5. Check Source Warnings

    Use the visible EPA/NSF source pointers and unresolved gaps to prepare questions for the designer, sanitarian, soil scientist, installer, and health department.

  6. Export a Review Worksheet

    Export a source-aware worksheet for internal planning. It is not a permit submittal, stamped design, health-department approval, product certification, or installation instruction.

Built For

  • Homeowners organizing septic questions before contacting the local health department
  • Designers and installers collecting source gaps before formal site-specific design
  • Real estate teams screening rural parcel questions without treating output as buildability proof
  • Contractors estimating planning ranges before bids, permits, and inspection requirements
  • Owners comparing conventional, mound, pressure, and ATU prompts before qualified review

Assumptions

  • Daily wastewater flow uses a local 150 GPD/bedroom prompt unless the user enters a manual planning value.
  • Soil and perc rows are source prompts and not a verified site evaluation.
  • Water-table, bedrock, setback, slope, reserve-area, and permit requirements remain unresolved.
  • System type is a planning prompt for residential domestic wastewater only.

Limitations

  • Does not determine local-code compliance, permit approval, system feasibility, repair acceptability, or drinking-water safety.
  • Does not model full hydraulics, distribution network, pump controls, dosing frequency, elevations, alarms, or maintenance contracts.
  • Does not replace soil morphology, perc testing, hydrogeologic assessment, product listing, or inspection.

References

  • EPA Types of Septic Systems source pointer
  • EPA Septic Systems and Drinking Water source pointer
  • EPA Onsite Wastewater Treatment Systems Manual source pointer
  • NSF residential wastewater treatment system certification source pointer

Frequently Asked Questions

No. It is a source-aware planning screen. Current state/county rules, site evaluation, permit conditions, product approvals, inspection, and qualified designer or sanitarian review control actual design.
Use the accepted local site-evaluation process, which may include perc testing, soil morphology, seasonal water-table indicators, bedrock, slope, and replacement-area review. The selector is not a soil report.
No. They are generic local prompts. Health departments can require different tank volumes, compartments, effluent filters, reserve areas, wells setbacks, surface-water setbacks, and inspection details.
No. ATU use depends on current certified listings, manufacturer instructions, local approval, effluent limits, power/alarm design, and maintenance contract requirements.
No. It is a rough planning prompt. Excavation, rock, groundwater, access, pumps, electrical, permits, products, local labor, and contractor bids control actual cost.
Treat it as a review flag. A mound, pressure distribution, advanced treatment, or denial may be required, but only local rules and qualified site-specific design decide the outcome.
Disclaimer: This screen provides preliminary source-aware onsite wastewater prompts only. It is not a permit design, health-department approval, soil evaluation, public-health determination, product certification, installation instruction, inspection result, or substitute for qualified local review.

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