Insulation Calculator
Estimate blown-in insulation for an attic. Enter the area and your target R-value, and we'll approximate the number of bags. Coverage varies by product — always check the bag.
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Check it outR-value sets the coverage
Blown-in insulation is rated by how many square feet one bag covers at a given R-value — the higher the R-value (more insulation), the fewer square feet per bag. The estimates here are typical for cellulose; fiberglass and specific brands vary, so the bag's coverage chart is the final word. Higher R-values pay off most in cold climates and attics.
How it’s calculated
Bags = area ÷ coverage per bag, where coverage per bag falls as the target R-value rises.
Results update as you type and are estimates, not professional advice — verify important decisions with a qualified professional.
Worked example
A 40x30 attic targeting R-38 needs about 26 bags of blown-in insulation.
Common mistakes
- Using one product's coverage for another.
- Ignoring that coverage drops at higher R-values.
Where it is used
- Estimating bags for an attic insulation job.
- Comparing R-value targets by climate.
Frequently asked questions
What R-value do I need?
Attics commonly target R-38 in moderate climates and R-49 or more in cold ones. Check your local code and energy guidelines.
Why does coverage drop at higher R?
More insulation depth per square foot means each bag spreads over less area to reach the higher R-value.
Cellulose or fiberglass?
Both work blown-in. Cellulose is denser and made from recycled content; fiberglass is lighter. Coverage per bag differs, so verify on the label.
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