Blown-In Attic Insulation Bag Calculator
Estimate added attic R-value, installed depth, product-label coverage, bags, waste, and editable insulation material cost.
How to use the blown-in insulation calculator
- Measure the actual project. Break irregular work into separate sections and record finished dimensions consistently.
- Enter the core measurements. The quick view focuses on project geometry; add or subtract sections where the calculator supports multiple areas.
- Review purchasing assumptions. Open Advanced inputs to replace example prices, waste, coverage, density, pack size, minimum order, or delivery assumptions with current project information.
- Calculate and verify. Review the formula, limitations, whole-unit rounding, product instructions, and supplier requirements before purchasing.
Key inputs covered: Attic floor area, Uninsulated or excluded area, Target total R-value, Existing effective R-value, Selected product R-value per inch, Product-label coverage per bag at required R, Installation allowance, Bag example price.
Result coverage: The blown-in insulation calculator reports 6 separate quantities so the primary estimate and its supporting purchase or planning values can be checked together.
How the estimate works
Target R-value minus existing effective R-value gives the added target; added R divided by entered R per inch estimates depth, while net attic area divides by the selected product label's coverage per bag.
R-49 target minus R-19 existing insulation requires an added R-30 before using the selected product's coverage chart.
Assumptions, rounding, and limitations
Dimensions are treated as finished measurements. Only deductions and allowances entered above are included. Decimal measurements display to two places; purchase quantities round up when a whole container or piece is required.
- Enter the bag coverage printed for the selected product and required installed R-value; coverage is not constant across depths or products.
- Existing insulation condition, compression, settling, air leakage, ventilation, moisture, electrical clearances, combustion appliances, and access affect the project.
- Air-seal first where appropriate and follow current product instructions, local energy and fire codes, protective-equipment requirements, and qualified professional guidance.
Sources and review
These references support unit conversions and selected planning assumptions. Product instructions and local requirements control the actual project.
- NIST Handbook 44 — current unit-conversion tables
- U.S. Department of Energy Consumer Guide to Home Insulation
Last reviewed: 2026-10-09
Editorial process
BuildPlanCalc publishes the formula, editable assumptions, limitations, and supporting references so the estimate can be checked rather than treated as a black box. See the calculation and review methodology, or report a correction.
Frequently asked questions
Are the results exact?
No. Results are planning estimates based on the dimensions and assumptions entered. Confirm product coverage, site conditions, and ordering rules with the supplier.