Blown-In Insulation Calculator
Attic bags and installed depth from area and added R-value.
How it works
Added R-value is the target total minus the effective insulation already present. The calculator finds that value in the selected coverage chart, multiplies its minimum bags-per-1,000-ft² rate by the attic area and rounds up to whole bags.
Loose-fill performance requires both the chart's minimum bag count and its minimum depth. Existing insulation can be uneven or degraded, and interpolated values are planning estimates only. Verify the existing assembly and follow the current product bag, ventilation, clearance and installation instructions.
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How the Blown-In Insulation Calculator works
This US blown-in insulation calculator turns attic square footage and the R-value still needed into whole bags, an installed depth and a settled-depth check. It uses a manufacturer coverage chart instead of assuming one universal R-value per inch.
Calculate the R-value to add
Subtract the effective R-value already present from the target for the completed attic assembly. For example, an attic assessed at R-19 with a target of R-49 needs an added R-30. The calculator then reads the R-30 row, not the R-49 row, because the existing insulation remains part of the assembly.
This subtraction is only as reliable as the existing-layer assessment. Loose fill may be uneven, compressed, damp or displaced by storage and service work. Identify the material, measure several locations and follow local requirements when setting the target.
Minimum bags and depth must both be met
Owens Corning's AttiCat chart lists minimum bags per 1,000 square feet, maximum net coverage per bag and minimum thickness. The calculator uses the bag-rate column for quantity, rounds up to whole bags and shows depth as a separate field check.
For 1,000 square feet at an added R-30, the chart rate is 14.6 bags and the minimum thickness is 10.75 inches, so the purchase is 15 full bags before any optional reserve. Installing fewer bags cannot be corrected merely by making a small area look deeper.
Use the exact bag chart
AttiCat rows from R-13 through R-60 are included as a planning profile. When the requested added R-value falls between published rows, the page clearly marks the depth and bag rate as interpolated; select a listed row before installation.
The custom mode accepts one complete row from another product bag. Keep the row together: loose-fill products do not share a universal bag yield, R per inch or settlement allowance. Also follow the product's machine settings, ventilation baffles, heat-source clearances and personal-protection instructions.
FAQ
How many bags of blown-in insulation do I need for 1,000 sq ft at R-30? expand_more
The current AttiCat chart lists 14.6 bags per 1,000 sq ft at R-30. The calculator rounds that to 15 whole bags and shows a minimum installed depth of 10.75 inches.
How do I account for insulation already in the attic? expand_more
Enter its assessed effective R-value and the target total. The calculator uses the difference. For existing R-19 and target R-49, it calculates an added R-30; confirm that the old layer is dry, even and correctly identified.
Does the depth alone prove the R-value? expand_more
No. The coverage chart requires the minimum material quantity as well as the minimum depth. Bag count is a weight check, while depth helps confirm an even installation.