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Area to cover divided by the coverage each bag or roll provides, per the product label.
A higher R-value batt or a thicker layer of blown-in insulation covers less area per bag than a lower R-value product, since more material is packed into the same bag — always use the coverage figure from your specific product's label, not a generic estimate.
Attics typically use loose-fill blown insulation measured by bag coverage at a target depth; walls typically use batts measured by square footage of cavity — this calculator's simple area-and-coverage approach works for either, as long as you use the right product's coverage rate.
Bags/rolls needed
13
Coverage per unit varies a lot by R-value and product — check the specific bag or roll's label.
What you entered
Divide area by coverage per unit
500 ÷ 40= 12.5 unitsRound up to a whole number of units
⌈12.5⌉= 13 unitsResult
Bags/rolls needed: 13
500 sq ft needs 13 bags or rolls at 40 sq ft coverage each.