Insulation calculator

1. Area
   length × width
   40' 0" × 25' 0" = 1,000.00 SF
2. Bags
   area ÷ maximum SF per bag at this R-value, rounded up
   1,000.00 SF ÷ 14.1 SF = 71

Where the numbers come from

• Batts per bag: SF per bag = pieces × width × length ÷ 144 — R-13 15" × 93" × 11 = 106.56 SFJohns Manville Fiberglass Manufacturers Fact Sheet (BID-380 12/19): every row is this math (R-30 16" × 48" × 11 = 58.66 SF, R-19 15" × 93" × 9 = 87.18 SF). The calculator counts batts by framing bay: a 15" batt fills a 16" bay, so one batt covers 16" × its length of wall. Plates, headers and blocking are not taken off, so the count runs a little high. Other brands pack differently — use your bag.Source
• Blown cellulose chart: Greenfiber Sanctuary 25 lb bag: R-30 = 25.9 SF/bag, 8.3" settled · R-38 = 19.0, 10.4" · R-49 = 14.1, 13.3" · R-60 = 11.6, 16.1"Attic card PM-6.3330-SDBZ Rev A 04/26, loose-fill, net coverage with no framing adjustment. The chart checks itself: 25 lb ÷ 1.32 lb/SF = 18.9 ≈ 19.0 SF at R-38, and 1,000 ÷ 19.0 = 52.6 bags per 1,000 SF. Blow it at least 11.2" initially to settle to 10.4". Both the bag count and the thickness must be met for the R-value.Source
• Blown fiberglass chart: Owens Corning AttiCat 28.5 lb bag: R-30 = 65.4 SF/bag, 10¼" · R-38 = 51.4, 13" · R-49 = 38.8, 16½" · R-60 = 31.1, 20"Pub. No. 10009393-C (28.5 lb bag): 28.5 lb ÷ 0.554 lb/SF = 51.4 SF at R-38. Settling is negligible for this product. Bag weights change between editions — if your bag weighs something else, pick "From the bag" and type the chart number.Source
• Bag coverage chart: Bags = area ÷ maximum SF per bag at the R-valueThe FTC R-value Rule (16 CFR 460.12) requires every loose-fill bag to print, for R-13, 19, 22, 30, 38 and 49 at least, the minimum settled thickness, initial installed thickness, maximum net coverage, bags per 1,000 SF and minimum weight per SF. Use those numbers.Source
• Attic R-value by climate zone: 2021 IECC: zone 1 = R-30, zones 2–3 = R-49, zones 4–8 = R-60Ceiling column of 2021 IECC Table R402.1.3, as listed by ENERGY STAR. Your local code may be an older or amended edition — check with the building department.Source