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Blown In Insulation Calculator
Quick answer: Divide your attic area by the bag coverage printed on the product's bag chart for the R-value you want, then add a waste allowance. Bag coverage changes with the target R, so always use the chart row for your level. The result is a planning count; buy a few extra bags and return unopened ones if the store allows.
How it works
Bags = area ÷ coverage per bag at your R × (1 + waste %). Loose-fill makers publish a coverage chart on each bag listing, for each R-value, the minimum bags per 1,000 sq ft, the coverage per bag, the installed thickness and the minimum settled thickness. Our default coverage is just an example value to show the math; replace it with your bag's figure. Use the attic insulation calculator to find the R to add, and depth markers to check depth while blowing.
Worked example
Figures below are illustrative examples (2026-10-29), not quotes or guarantees.
Assumptions: 1,000 sq ft, adding R38, an assumed coverage of 40 sq ft per bag at R38, 10% waste. Bags = 1,000 ÷ 40 × 1.10 = 27.5, round up to 28.
FAQ
Why does coverage fall as R rises?
Higher R needs a deeper layer, so each bag covers less area.
Do I need a machine?
Yes, loose-fill needs a blowing machine; see machine rental.
Is installed depth the same as settled depth?
No. Some products settle; the bag lists both.
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