Insulation Calculator â How Many Bags Do I Need?
Enter the area you're insulating and pick a target R-value to get the bag count for blown-in insulation. No sign-up, no data stored.
Insulation bags
How the bag count is calculated
- Area = length à width of the surface you're insulating (attic floor, wall, etc.).
- Coverage: blown-in fiberglass bags cover less at higher R-values â about 150 sq ft at R-13 down to 55 sq ft at R-49.
- Bags = area ÷ coverage per bag, rounded up, plus ~5% for settling and odd spaces.
Coverage varies by brand and machine settings â the bag label always lists coverage at the depth you need. Blown-in settles over time, so topping up a few years after install is normal.
R-value & coverage reference
What each surface typically needs, and the loose-fill coverage per bag.
| Surface | Typical R-value | Coverage per bag |
|---|---|---|
| Exterior walls | R-13 to R-23 | ~110â150 sq ft |
| Floors (unheated) | R-19 to R-30 | ~88â110 sq ft |
| Attic / ceiling | R-38 to R-49 | ~55â71 sq ft |
| Crawl space / basement walls | R-11 to R-25 | ~110â150 sq ft |
Last updated: October 2026 · Coverage figures are typical for blown-in fiberglass loose fill. Always use the coverage printed on the bag at your target R-value, and check your climate zone's recommended R-value.
Insulation calculator FAQ
About 14 bags at R-38 (1,000 ÷ 71 â 14), or 11 bags at R-30. Add ~5% for settling if you want margin.
Roughly 150 sq ft at R-13, 110 at R-19, 88 at R-30, 71 at R-38, and 55 at R-49 for blown-in fiberglass. Coverage depends on depth â check the label.
Most US homes need R-38 to R-49 for attics (10â16 in of fiberglass). Walls run R-13 to R-23 and floors over unheated space R-19 to R-30.
Yes â blown-in requires renting a machine (about $50â100/day) plus bags at ~$0.50â1 per sq ft installed value. Batts are fully DIY for standard spacing.
Measure the existing depth, then add enough to reach your target R-value â don't count the old layer twice. If old insulation is wet or compressed, remove it first.