Insulation Calculator
Enter the area to insulate and the coverage printed on the bag to see how many bags or rolls to buy.
Results are estimates for planning only. Always confirm measurements, local codes and manufacturer specs before ordering materials or quoting a job. See our Terms.
How much insulation do I need?
Measure the area (length x width for attics, length x height for walls), add about 5% for cuts, and divide by the square feet each bag covers. Coverage depends on the product and R-value, so always use the number printed on the bag.
Typical targets in the US: R-13 to R-15 for 2x4 walls, R-19 to R-21 for 2x6 walls, R-30 for floors, and R-38 to R-60 for attics depending on climate. Check your local energy code.
Questions
What R-value do I need in my attic?
Most of the US calls for R-38 to R-60 in attics. Colder climates need the higher end.
Can I use the same calculator for blown-in insulation?
Yes, if you enter the coverage per bag for the depth you want. Blown-in bags list coverage for each R-value on the label.
Do I subtract windows and doors?
For walls, yes: subtract the area of large windows and doors. For attics, use the full floor area.