Insulation is sold by coverage at a given R-value, and the chart on the bag tells you how far one bag goes. Start with the target R for your zone.
Insulation calculator
Pick your climate zone and where you are insulating, then enter the coverage from the bag.
Enter your numbers to see the result.
Recommended R-values (ENERGY STAR)
| Zone | Attic, little or none | Attic with 3 to 4 in | Floor |
|---|---|---|---|
| 1 | R30 | R25 | R13 |
| 2 | R49 | R38 | R13 |
| 3 | R49 | R38 | R19 |
| 4A, 4B | R60 | R49 | R19 |
| 4C, 5, 6 | R60 | R49 | R30 |
| 7, 8 | R60 | R49 | R38 |
These are ENERGY STAR's recommendations for existing wood-framed homes, based on the 2021 International Energy Conservation Code. Find your zone on the ENERGY STAR map; your local code may require more.
Reading the bag
Blown-in bags list how many square feet one bag covers at each R-value (and the depth to blow). Batts list the square feet per roll or bag. Enter the figure for your target R and the calculator rounds up to whole bags.
Sources
Sources last checked 1 November 2026.
Frequently asked questions
What R-value should my attic be?
R49 to R60 in most of the US, per ENERGY STAR; R30 in zone 1.
How many bags of blown-in insulation do I need?
Divide the attic floor area by the coverage per bag at your target R from the bag chart, and round up.