{
  "slug": "gutter-sizing",
  "title": "Gutter Sizing Calculator",
  "heading": "Gutter & Downspout Sizing Calculator",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/gutter-sizing",
  "summary": "Required gutter capacity and downspout count for your roof.",
  "description": "Gutter size follows the adjusted roof area: drainage area times rainfall intensity. A single 3 in downspout drains roughly 600 sq ft of roof in heavy rain.",
  "formula": "Adjusted area = roof area × pitch factor; downspouts = area ÷ capacity per spout.",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=gutter-sizing",
  "inputs": [
    {
      "id": "area",
      "label": "Roof footprint area",
      "kind": "number",
      "hint": null,
      "default": 1800,
      "unit": "sq ft",
      "min": 50,
      "max": null
    },
    {
      "id": "pitch",
      "label": "Roof pitch (rise per 12)",
      "kind": "number",
      "hint": null,
      "default": 6,
      "unit": "in",
      "min": 0.5,
      "max": 24
    },
    {
      "id": "rain",
      "label": "Peak rainfall intensity",
      "kind": "number",
      "hint": null,
      "default": 5,
      "unit": "in/hr",
      "min": 1,
      "max": 12
    }
  ],
  "outputs": [
    {
      "id": "gutterIn",
      "label": "Recommended gutter size (in)",
      "format": "number",
      "hint": null,
      "primary": true
    },
    {
      "id": "spouts3",
      "label": "3 in downspouts needed",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "spouts4",
      "label": "4 in downspouts needed",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "adj",
      "label": "Pitch-adjusted roof area",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "drainage",
      "label": "Design drainage area",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "gpm",
      "label": "Peak flow (gal/min)",
      "format": "decimal",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Roof footprint area: 1800 sq ft",
      "Roof pitch (rise per 12): 6 in",
      "Peak rainfall intensity: 5 in/hr"
    ],
    "outputs": [
      "Recommended gutter size (in): 5",
      "3 in downspouts needed: 4",
      "4 in downspouts needed: 2",
      "Pitch-adjusted roof area: 1,980",
      "Design drainage area: 1,980",
      "Peak flow (gal/min): 103"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter roof footprint area (sq ft).",
      "Enter roof pitch (rise per 12) (in).",
      "Enter peak rainfall intensity (in/hr).",
      "Read your recommended gutter size (in) 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": 1080,
        "pitch": 3.5999999999999996,
        "rain": 3
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "area": 1800,
        "pitch": 6,
        "rain": 5
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "area": 2880,
        "pitch": 9.600000000000001,
        "rain": 8
      }
    }
  ],
  "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 gutter & downspout sizing calculator work?",
      "a": "Gutter size follows the adjusted roof area: drainage area times rainfall intensity. A single 3 in downspout drains roughly 600 sq ft of roof in heavy rain. The underlying maths is: Adjusted area = roof area × pitch factor; downspouts = area ÷ capacity per spout."
    },
    {
      "q": "What do I need to enter?",
      "a": "3 values: roof footprint area, roof pitch (rise per 12), and peak rainfall intensity. 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 recommended gutter size (in) 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/roof-pitch",
    "https://www.revenuelab.fyi/toolbox/rain-barrel"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Gutter Sizing Calculator (https://www.revenuelab.fyi/toolbox/gutter-sizing)"
}