The formula is simple — here's how to count bags for walls, attics, and floors, with a quick reference table by house size.
Every bag of insulation lists its coverage in square feet at the specified R-value. To find your quantity: measure the area you're insulating (wall face area, attic floor area, etc.), divide by the coverage per bag, and add 10–15% for waste and cuts. That's your order quantity.
| Product | Batt Width | Coverage / Bag | Bags per 1,000 sq ft |
|---|---|---|---|
| R-11 (3.5") | 15" or 23" | ~75–90 sq ft | ~12–14 bags |
| R-13 (3.5") | 15" or 23" | ~75–90 sq ft | ~12–14 bags |
| R-15 HD (3.5") | 15" or 23" | ~70–80 sq ft | ~13–15 bags |
| R-19 (6.25") | 15" or 23" | ~48–55 sq ft | ~19–22 bags |
| R-21 HD (5.5") | 15" or 23" | ~45–55 sq ft | ~19–23 bags |
| R-30 (9.5–10") | 15" or 23" | ~40–48 sq ft | ~21–25 bags |
| R-38 (12") | 15" or 23" | ~32–40 sq ft | ~25–32 bags |
| R-49 (16") | 15" or 23" | ~25–32 sq ft | ~32–40 bags |
Coverage varies by manufacturer. Confirm coverage on the specific product bag before ordering. These ranges are typical across common manufacturers we stock.
Project: 2×6 exterior walls on a 2,000 sq ft house. Ordering R-21 HD. Assume coverage of 50 sq ft per bag.
| House Size | R-13 Walls (est.) | R-21 Walls (est.) | R-38 Attic (est.) |
|---|---|---|---|
| 1,200 sq ft | 20–25 bags | 22–28 bags | 35–45 bags |
| 1,800 sq ft | 28–35 bags | 30–40 bags | 50–65 bags |
| 2,500 sq ft | 38–48 bags | 42–55 bags | 70–90 bags |
| 3,500 sq ft | 52–65 bags | 58–75 bags | 95–125 bags |
These estimates assume 8–9 ft ceilings, 20% opening deduction for walls, and full attic floor coverage. Use our bag calculator for a precise number based on your actual measurements, or call us with your square footage and we'll figure it out together.
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