Free estimate — verify against local code before building
Insulation Bags & Batts Calculator
Choose the exact product chart or copy its label coverage—generic R-per-inch math is not accurate enough to order insulation.
What this calculator includes
Estimate bags or packages using the coverage printed for the exact product and target R-value. For uninsulated attics, the built-in starting points follow DOE's published 2021 IECC table: R-30 in zone 1, R-49 in zones 2–3, and R-60 in zones 4–8. Wall and floor requirements depend on the complete assembly, so those targets must be entered from approved project documents. Local adoption, amendments, existing insulation, assembly details, compression, air sealing, ventilation, moisture control, and product instructions still require verification before purchase or installation.
How to use this insulation calculator
- 01
Confirm the target assembly
Use the attic table only as the stated 2021 IECC starting point. For walls and floors, enter the target from approved plans or the building department.
- 02
Choose the exact product data
Use the built-in AttiCat open-attic chart only for that product, or copy coverage, R-value, and minimum thickness from the exact package label.
- 03
Enter net area and allowance
Measure the net insulated surface. Add a purchase allowance only when project conditions justify it; package count rounds up once at the end.
- 04
Verify site conditions
Air-seal first and check clearances, ventilation, vapor-control strategy, existing insulation, access, and manufacturer instructions before installation.
Calculation sources and review
Primary references and formula assumptions are linked so you can verify them against the selected product, supplier, and adopted local requirements.
Internal formula review completed July 13, 2026. What this review covers
- U.S. DOE — 2021 IECC insulation and air-sealing table (opens in a new tab)
Publishes attic ceiling R-30 for zone 1, R-49 for zones 2–3, and R-60 for zones 4–8.
- DOE Building America climate-specific assemblies (opens in a new tab)
Shows why complete wall, roof, and foundation assemblies—not a single cavity R-value—must be evaluated.
- Owens Corning AttiCat product and coverage chart (opens in a new tab)
Source for the built-in open-attic coverage and minimum-thickness rows.
Frequently asked questions
What attic R-value does the 2021 IECC table show?
DOE's published table shows R-30 in climate zone 1, R-49 in zones 2 and 3, and R-60 in zones 4 through 8 for a ceiling under an uninsulated attic. Local code and alternative assemblies can differ.
Why does this calculator ask for label coverage?
Loose-fill and batt products vary by material, bag weight, density, machine, target R-value, and package size. A generic R-per-inch or inverse-coverage formula can under-order material.
How does the AttiCat preset calculate bags?
It uses the current manufacturer chart's maximum net coverage per bag and minimum thickness for the selected R-30, R-49, or R-60 row, multiplies area by any entered allowance, divides by coverage, and rounds up.
Will the calculator automatically layer batts to reach a higher R-value?
No. Automatic layering was removed because cavity size, compression, facing, orientation, thermal bridging, and assembly approval matter. The tool flags a selected product below the entered target.
How many attic baffles do I need?
Count the vented rafter bays that actually require chutes. Floor area alone cannot determine that count, so the calculator never invents a one-per-square-foot rule.