Blown In Insulation Calculator
A blown in insulation calculator finds how many bags of loose-fill insulation you need by dividing your attic area by the coverage of one bag at your target R-value. Each bag lists its coverage at each R-value. Enter your attic area, target R-value and bag coverage below to get the bag count.
Enter the area and the bag's coverage at your target R-value.
How Many Bags of Blown In Insulation Do You Need?
To find blown-in bags, divide your attic square footage by the coverage one bag provides at your target R-value, a figure printed on every bag. At R-38, a bag might cover a certain number of square feet; a 1,000 square foot attic divided by that coverage gives the bag count. Because coverage drops as the R-value rises (more depth), the calculator uses the coverage you enter for your chosen R-value.
How Deep Should Blown In Insulation Be?
Blown-in insulation depth sets the R-value: each inch adds roughly R-2.5 to R-3.7 depending on the material (fiberglass or cellulose). To reach R-38 you need roughly 12 to 15 inches of loose fill. The bag coverage already accounts for this depth at each R-value, so use the bag's coverage figure for your target. The calculator turns that into the number of bags for your attic.
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Frequently asked questions
- How many bags of blown in insulation do I need?
- Divide your attic area by the bag's coverage at your target R-value, listed on the bag. A 1,000 square foot attic at R-38 uses the per-bag coverage to find the count.
- How deep should blown in insulation be?
- Roughly 12 to 15 inches to reach R-38, since each inch adds about R-2.5 to R-3.7. The bag coverage accounts for depth at each R-value.