Insulation Calculator
Enter the area you’re insulating and the coverage per package to get the number of batts or rolls to buy.
Enter your measurements to see what to buy.
How to calculate it
Enter the area you’re insulating and the coverage per package to get the number of batts or rolls to buy.
Source: Packages = total area with waste ÷ coverage per package. Coverage in ft² is printed on the bag and varies by R-value and thickness.
A 400 ft² attic at R-30 with 8% waste = 432 ft². A package covering 77 ft²: 432 ÷ 77 = 5.6 → 6 packages.
Want the full step-by-step walkthrough? Read our How Many Sheets of Drywall Do I Need?.
Purchasing & waste guidance
- Match the R-value to your climate zone — attics usually need R-38 to R-60.
- Batts are pre-cut for standard wall cavities; rolls are better for long attic runs.
- Add 5–10% waste for cuts around outlets, joists and odd cavities.
- Coverage per package is printed on the bag and shrinks as R-value (thickness) goes up.
Assumptions & what’s included
- Area is the total surface to insulate (wall, attic or ceiling).
- Coverage per package is the ft² printed on the bag for your chosen R-value.
- Waste allowance covers cuts and odd cavities. Price is per package and optional.
Frequently asked questions
How much insulation do I need for my attic?
Measure the attic floor area, pick the R-value for your climate (often R-38 to R-60), and divide the area plus 5–10% waste by the coverage printed on the package. The calculator does this for any package size.
What R-value should I use?
It depends on your climate zone. Most attics need R-38 to R-60, walls R-13 to R-21, and floors R-25 to R-30. Check the DOE recommendation for your zip code.
How many square feet does a package of insulation cover?
Coverage is printed on the bag and varies by R-value and thickness — a higher R-value means less coverage per package. Enter the exact number from the bag for an accurate count.
Related guides
Step-by-step project guides that use this calculator.