{
  "slug": "blown-in-insulation-bags-calculator",
  "title": "Blown-In Insulation Bags Calculator",
  "heading": "Blown-In Insulation Bags Calculator",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/blown-in-insulation-bags-calculator",
  "summary": "Convert attic square footage and target R-value into bags of blown-in insulation.",
  "description": "Blown-in insulation — whether cellulose or fiberglass — is sold in bags with a printed coverage chart showing how many square feet one bag covers at various depths and R-values, since blown-in material's insulating power depends on how thick a layer it's blown to. This calculator uses a simplified version of that chart: you enter your attic's square footage and your target R-value, and it estimates bags needed based on typical cellulose coverage rates (roughly 30-40 sq ft per bag at R-38, less at higher R-values like R-49 or R-60 since a deeper, denser layer is needed). Because manufacturers vary in exact bag coverage and settle differently over time, this is a solid planning estimate, but always cross-check against the specific bag's printed chart at the store, which lists exact square-foot coverage per bag for each target R-value and installed depth. Adding blown-in insulation over existing attic insulation to boost R-value is one of the most cost-effective energy upgrades a homeowner can make, and getting the bag count close before rental of a blower machine (often required with bulk bag purchases) avoids a second supply run mid-job.",
  "formula": "Bags = ceil((Attic Area ÷ Coverage per Bag at Target R-value) × 1.05 settling allowance).",
  "dateModified": "2026-09-06",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=blown-in-insulation-bags-calculator",
  "inputs": [
    {
      "id": "atticArea",
      "label": "Attic area",
      "kind": "number",
      "hint": null,
      "default": 1200,
      "unit": "sq ft",
      "min": 50,
      "max": null
    },
    {
      "id": "targetRValue",
      "label": "Target R-value",
      "kind": "select",
      "hint": null,
      "default": "R38",
      "options": [
        {
          "label": "R-38",
          "value": "R38"
        },
        {
          "label": "R-49",
          "value": "R49"
        },
        {
          "label": "R-60",
          "value": "R60"
        }
      ]
    }
  ],
  "outputs": [
    {
      "id": "bags",
      "label": "Bags needed",
      "format": "number",
      "hint": null,
      "primary": true
    },
    {
      "id": "coveragePerBag",
      "label": "Coverage per bag at target R-value",
      "format": "number",
      "hint": "sq ft",
      "primary": false
    },
    {
      "id": "rawBags",
      "label": "Exact bags before rounding",
      "format": "decimal",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Attic area: 1200 sq ft",
      "Target R-value: R-38"
    ],
    "outputs": [
      "Bags needed: 36",
      "Coverage per bag at target R-value: 35",
      "Exact bags before rounding: 36"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter attic area (sq ft).",
      "Enter target r-value.",
      "Read your bags needed 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": {
        "atticArea": 700,
        "targetRValue": "R38"
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "atticArea": 1200,
        "targetRValue": "R38"
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "atticArea": 1900,
        "targetRValue": "R38"
      }
    }
  ],
  "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 many bags of blown-in insulation do I need for an attic?",
      "a": "It depends heavily on target R-value and depth — a typical R-38 attic needs roughly one bag per 30-35 sq ft, while a deeper R-60 layer needs closer to one bag per 20-22 sq ft since more material is packed into the same footprint."
    },
    {
      "q": "Should I use the printed bag chart instead of a general estimate?",
      "a": "Yes, always cross-check with the specific product's coverage chart printed on the bag, since cellulose, fiberglass, and different manufacturers' densities vary the exact square-foot coverage per bag at a given R-value."
    },
    {
      "q": "Can I blow insulation over existing attic insulation?",
      "a": "Yes, this is one of the most common and cost-effective ways to boost attic R-value, as long as the existing insulation is dry and not compressed or contaminated, in which case it may need removal first."
    },
    {
      "q": "Do I need to rent a blower machine to install blown-in insulation?",
      "a": "Most home centers offer free or low-cost blower machine rental with the purchase of a minimum number of bags, which is usually the more economical route versus hiring a contractor for a straightforward attic top-up."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/insulation-batts-calculator",
    "https://www.revenuelab.fyi/toolbox/drywall-sheets-calculator",
    "https://www.revenuelab.fyi/toolbox/roofing-squares-calculator"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Blown-In Insulation Bags Calculator (https://www.revenuelab.fyi/toolbox/blown-in-insulation-bags-calculator)"
}