{
  "slug": "rain-barrel",
  "title": "Rainwater Harvest Calculator",
  "heading": "Rainwater Collection & Barrel Sizing Calculator",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/rain-barrel",
  "summary": "Gallons captured per storm and per year from your roof.",
  "description": "One inch of rain on 1,000 sq ft of roof yields about 623 gallons before losses. Collection efficiency of 85% is a realistic planning number.",
  "formula": "Gallons = area × inches × 0.623 × efficiency.",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=rain-barrel",
  "inputs": [
    {
      "id": "area",
      "label": "Roof catchment area",
      "kind": "number",
      "hint": null,
      "default": 1200,
      "unit": "sq ft",
      "min": 50,
      "max": null
    },
    {
      "id": "storm",
      "label": "Rain per storm",
      "kind": "number",
      "hint": null,
      "default": 1,
      "unit": "in",
      "min": 0.1,
      "max": null
    },
    {
      "id": "annual",
      "label": "Annual rainfall",
      "kind": "number",
      "hint": null,
      "default": 38,
      "unit": "in",
      "min": 1,
      "max": null
    },
    {
      "id": "eff",
      "label": "Collection efficiency",
      "kind": "number",
      "hint": null,
      "default": 85,
      "unit": "%",
      "min": 30,
      "max": 100
    },
    {
      "id": "use",
      "label": "Garden use per week",
      "kind": "number",
      "hint": null,
      "default": 60,
      "unit": "gal",
      "min": 0,
      "max": null
    }
  ],
  "outputs": [
    {
      "id": "storm",
      "label": "Gallons per storm",
      "format": "decimal",
      "hint": null,
      "primary": true
    },
    {
      "id": "yearly",
      "label": "Gallons per year",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "barrels",
      "label": "55-gal barrels to hold one storm",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "weeks",
      "label": "Weeks of garden watering",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "monthly",
      "label": "Average gallons per month",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "savings",
      "label": "Water bill savings per year",
      "format": "currency",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Roof catchment area: 1200 sq ft",
      "Rain per storm: 1 in",
      "Annual rainfall: 38 in",
      "Collection efficiency: 85 %",
      "Garden use per week: 60 gal"
    ],
    "outputs": [
      "Gallons per storm: 635",
      "Gallons per year: 24,147",
      "55-gal barrels to hold one storm: 12",
      "Weeks of garden watering: 10.6",
      "Average gallons per month: 2,012",
      "Water bill savings per year: $178"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter roof catchment area (sq ft).",
      "Enter rain per storm (in).",
      "Enter annual rainfall (in).",
      "Enter collection efficiency (%).",
      "Enter garden use per week (gal).",
      "Read your gallons per storm 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": {
        "area": 720,
        "storm": 0.6,
        "annual": 23,
        "eff": 51,
        "use": 35
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "area": 1200,
        "storm": 1,
        "annual": 38,
        "eff": 85,
        "use": 60
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "area": 1920,
        "storm": 1.6,
        "annual": 61,
        "eff": 100,
        "use": 95
      }
    }
  ],
  "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 rainwater collection & barrel sizing calculator work?",
      "a": "One inch of rain on 1,000 sq ft of roof yields about 623 gallons before losses. Collection efficiency of 85% is a realistic planning number. The underlying maths is: Gallons = area × inches × 0.623 × efficiency."
    },
    {
      "q": "What do I need to enter?",
      "a": "5 values: roof catchment area, rain per storm, annual rainfall, collection efficiency, and garden use per week. 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 gallons per storm result mean?",
      "a": "It is returned as a decimal 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/gutter-sizing",
    "https://www.revenuelab.fyi/toolbox/sprinkler-run-time"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Rainwater Harvest Calculator (https://www.revenuelab.fyi/toolbox/rain-barrel)"
}