Calculators/ Interior/Insulation Calculator
Insulation Calculator
Batt packs or blown-in bags for walls and attics.
Insulation is sold by coverage area, not by the cavity, so the pack count depends on the product rather than on your framing. Compression is the thing to watch: a batt squeezed into a shallow cavity loses much of the R-value printed on the bag.
How this is calculated
- Net area = length × width, minus any openings such as windows or attic hatches.
- Divide by the coverage printed on the pack. R-13 wall batts typically cover 40 square feet per pack; blown-in coverage falls as the target R-value rises.
- Add 5% waste. Batts cut around outlets and pipes always leave unusable offcuts.
Frequently asked questions
What R-value do I need?
It depends on climate zone. US attics typically want R-38 to R-60, walls R-13 to R-21, and floors over unheated space R-25 to R-30. Check your local energy code.
Can I compress insulation to fit?
No. Compressing a batt reduces its R-value, sometimes sharply. Use a batt sized for the cavity depth, or switch to a higher-density product.
Is blown-in better than batts?
For attics, usually yes: it fills irregular spaces and around obstructions where batts leave gaps. For open stud walls, batts are easier and perform comparably when installed carefully.