What does this tool do?
Insulation is ordered from the coverage printed for each R-value and bag. This calculator uses typical bag coverage for common fiberglass batts, adds a 5% waste allowance and shows the nominal thickness.
The Formula
Bags = ⌈Area × (1 + Waste ÷ 100) ÷ Coverage per bag⌉Frequently Asked Questions
How many bags of R-13 insulation?
R-13 batts cover about 88 sq ft per bag, so 1,000 sq ft needs about 12 bags.
Can I compress insulation to fit?
No. Compression reduces the R-value; choose a product that fills the cavity at its rated thickness.