Attic Insulation Calculator — R-Value & Bags
Estimate existing and added attic R-value, then calculate bags, rolls, or batt packages from product coverage.
Attic insulation planning compares an estimated existing R-value with a target R-value, then divides the attic area by the product coverage stated for that added R-value. Climate zone is a reference, while the selected product chart determines the actual package count.
1,000 sq ft · estimated existing R-10 · add about R-39 to reach R-49.
- Attic insulation25 bags
Use the exact coverage chart on the selected product for the added R-value. Coverage per bag or package changes with target R-value, density, and installation method.
Air-seal safely before adding insulation, keep required ventilation and clearances open, and stop for moisture, damaged wiring, combustion appliances, suspected asbestos/vermiculite, or other hazards.
Step by step
- 1
Measure attic area and identify the existing insulation material and average settled depth without disturbing hazardous or concealed materials.
- 2
Compare the estimated existing R-value with an ENERGY STAR planning target for the climate zone, then choose the added R-value.
- 3
Enter the bag, roll, or batt coverage printed for that exact added R-value and verify air sealing, ventilation, electrical clearances, moisture, and safety before installation.
Check the estimate before you buy
Estimate existing attic R-value, additional R-value needed, and full insulation bags, rolls, or batt packages using product coverage.
A 1,000 sq ft attic with about 4 in of existing loose fiberglass is estimated near R-10 using a 2.5-per-inch planning value. To reach R-49, add about R-39. If the selected product covers 40 sq ft per bag at that installed R-value, the order rounds to 25 bags.
How the calculation works
Existing R-value is estimated from material depth and a conservative per-inch planning factor. The tool subtracts that estimate from the selected target, then divides attic area by the package coverage stated for that exact added R-value.
Attic Insulation Calculator — R-Value & Bags FAQ
Should I buy exactly the calculated amount of insulation?
Usually no. Cuts, spillage, breakage, uneven surfaces, batch matching, and package rounding can increase the order. Use the editable allowance and confirm the product label.
Why does the result round up?
Stores sell full bags, boxes, cans, rolls, panels, or pieces. The tool keeps the mathematical amount visible, then rounds the purchasing quantity up separately.
What attic R-value should I target?
ENERGY STAR publishes climate-zone planning recommendations, but the right assembly also depends on current insulation, local energy code, moisture, ventilation, space, and professional assessment.
Can I calculate bags from thickness alone?
Not reliably. Blown products use package charts that connect bag count, settled thickness, coverage, and installed R-value. Enter the coverage listed for the R-value you actually need.
Reference: ENERGY STAR recommended home insulation R-values. Results are practical estimates; complete labels, package directions, product specifications, and qualified professional advice take priority.