{
  "slug": "septic-tank-size",
  "title": "Septic Tank Size Calculator",
  "heading": "Septic Tank Sizing & Pump-Out Calculator",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/septic-tank-size",
  "summary": "Tank gallons by bedrooms plus pump-out interval.",
  "description": "Most jurisdictions require at least 1,000 gallons for a three-bedroom home and add 250 gallons per extra bedroom. Pump-out interval falls fast as household size grows.",
  "formula": "Gallons = base (bedrooms) ; interval ≈ tank ÷ (people × daily solids accumulation).",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=septic-tank-size",
  "inputs": [
    {
      "id": "bedrooms",
      "label": "Bedrooms",
      "kind": "number",
      "hint": null,
      "default": 3,
      "unit": null,
      "min": 1,
      "max": 10
    },
    {
      "id": "people",
      "label": "People in household",
      "kind": "number",
      "hint": null,
      "default": 4,
      "unit": null,
      "min": 1,
      "max": 15
    },
    {
      "id": "gpd",
      "label": "Water use per person",
      "kind": "number",
      "hint": null,
      "default": 60,
      "unit": "gal/day",
      "min": 20,
      "max": 150
    },
    {
      "id": "cost",
      "label": "Pump-out cost",
      "kind": "number",
      "hint": null,
      "default": 425,
      "unit": "$",
      "min": 0,
      "max": null
    }
  ],
  "outputs": [
    {
      "id": "size",
      "label": "Minimum tank size (gal)",
      "format": "number",
      "hint": null,
      "primary": true
    },
    {
      "id": "years",
      "label": "Years between pump-outs",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "months",
      "label": "Months between pump-outs",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "daily",
      "label": "Daily wastewater (gal)",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "retention",
      "label": "Retention time (days)",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "annualCost",
      "label": "Amortized pumping cost per year",
      "format": "currency",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Bedrooms: 3",
      "People in household: 4",
      "Water use per person: 60 gal/day",
      "Pump-out cost: 425 $"
    ],
    "outputs": [
      "Minimum tank size (gal): 1,500",
      "Years between pump-outs: 6.9",
      "Months between pump-outs: 83",
      "Daily wastewater (gal): 240",
      "Retention time (days): 6.3",
      "Amortized pumping cost per year: $61"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter bedrooms.",
      "Enter people in household.",
      "Enter water use per person (gal/day).",
      "Enter pump-out cost ($).",
      "Read your minimum tank size (gal) on the right — it updates as you type.",
      "Hit Share to keep the scenario or send it to someone."
    ]
  },
  "scenarios": [
    {
      "name": "Conservative",
      "description": "Lower-end numbers — what if things land soft?",
      "values": {
        "bedrooms": 2,
        "people": 2,
        "gpd": 35,
        "cost": 250
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "bedrooms": 3,
        "people": 4,
        "gpd": 60,
        "cost": 425
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "bedrooms": 5,
        "people": 6,
        "gpd": 95,
        "cost": 675
      }
    }
  ],
  "limitations": [
    "Estimates assume standard, average conditions — local rules, pricing, and materials vary.",
    "Results are rounded for readability; add a buffer before ordering, booking, or committing.",
    "Double-check anything with a real cost attached against a local quote."
  ],
  "faq": [
    {
      "q": "How does the septic tank sizing & pump-out calculator work?",
      "a": "Most jurisdictions require at least 1,000 gallons for a three-bedroom home and add 250 gallons per extra bedroom. Pump-out interval falls fast as household size grows. The underlying maths is: Gallons = base (bedrooms) ; interval ≈ tank ÷ (people × daily solids accumulation)."
    },
    {
      "q": "What do I need to enter?",
      "a": "4 values: bedrooms, people in household, water use per person, and pump-out cost. Each field starts with a sensible default, so you can change one number at a time and watch the result move."
    },
    {
      "q": "What does the minimum tank size (gal) result mean?",
      "a": "It is returned as a whole number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds."
    },
    {
      "q": "Is this calculator free, and do I need an account?",
      "a": "Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser."
    },
    {
      "q": "How accurate is the result?",
      "a": "It applies the standard formula exactly, so the arithmetic is precise. Estimates assume standard, average conditions — local rules, pricing, and materials vary."
    },
    {
      "q": "Who is this tool for?",
      "a": "It's built for anyone doing everyday planning maths — a quick estimate that would otherwise need four browser tabs and a calculator app."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/water-heater-cost",
    "https://www.revenuelab.fyi/toolbox/pipe-flow-rate"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Septic Tank Size Calculator (https://www.revenuelab.fyi/toolbox/septic-tank-size)"
}