Insulation Calculator
Interior · Updated July 2026
Enter the area you're insulating and the coverage per bag or roll to find how many you need for your walls, attic, or floor.
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Estimates only. Add extra for waste and confirm with your supplier.
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How much insulation do I need?
Divide the area to insulate by the coverage printed on each bag or roll, then round up. Check the R-value meets your climate's requirements.
Matching R-value to the space
Attics typically need R-38 to R-60 and walls R-13 to R-21, depending on your climate zone. Higher R-value batts cover less area per bag, so size your order to the R-value you actually need.
Batts vs. blown-in
Batts suit open stud and joist bays; blown-in loose fill is better for attics and irregular cavities. Divide the area you're insulating by the coverage on the bag to get the number of bags.
How to use this calculator
- 1Measure the area you're insulating in square feet.
- 2Find the coverage per bag or roll on the packaging.
- 3The calculator gives the number of units to buy.
Frequently asked questions
How is insulation coverage measured?
Bags and rolls list coverage in square feet at a target R-value; higher R-values cover less area per unit.
How much insulation do I need for my attic?
Most attics need R-38 to R-60; divide the attic area by the coverage per bag at that R-value.
How is insulation coverage measured?
Bags list coverage in square feet at a target R-value — higher R-value means less area per bag.
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