Insulation Calculator – Batts, Bags & R-Value

It depends on area and target R-value — the tool deducts framing, applies 5% waste, and converts net area into batt bundles or blown-cellulose bags with installed thickness. For example, a 1,200 sq ft attic at R-38 needs about 40 bags of blown cellulose.

About 40 bags: (1,200 ÷ 1,000) × 31 × 1.05 ≈ 40 bags of 30-lb cellulose, settling to roughly 13 in thick. The tool runs this math for any area and R-value.

DOE recommends R-38 to R-49 for attics in most US climate zones (R-30 minimum in hot zones 1–2); walls run R-13 to R-15 in 2×4 and R-19 to R-21 in 2×6 framing.

R-19 batt bundles cover about 88 sq ft each — a 1,000 sq ft wall (900 net after the 10% framing deduction) needs 11 bundles with waste. Framing spacing picks batt width: 15-in batts for 16 in O.C., 23-in for 24 in O.C.

Batt bundle coverage runs ~125 sq ft/bag at R-13 down to ~32 sq ft/bag at R-49; blown cellulose runs about 1.13 bags per 1,000 sq ft per R point (R-49 ≈ 55 bags/1,000 sq ft at 13.6 in settled). The tool compares both from your target R-value.