Blown-In Insulation Calculator
Enter your area and target R-value to get an instant estimate of bags needed. Choose between blown cellulose and blown fiberglass.
Blown-In Details
Bag coverage is a planning estimate based on settled depth. Always check the coverage chart printed on your specific product bag before purchasing. Cellulose: ~0.82 cu ft/bag (25 lb). Fiberglass: ~1.5 cu ft/bag (30 lb).
Cellulose vs Fiberglass at Your Target R-value
| Material | R/inch | Depth needed | Volume (cu ft) | Bags needed |
|---|
Formula
additional_R = max(0, target_R − existing_R)
depth_in = additional_R ÷ R_per_inch
volume_cuft = (area_sqft × depth_in) ÷ 12
bags = ⌈volume_cuft ÷ cu_ft_per_bag⌉
Related Calculators
- Insulation Calculator — full multi-material tool with zone lookup
- Attic Insulation Calculator
- R-Value Calculator
- DOE Climate Zone R-Value Reference
Frequently Asked Questions
For a 1,000 sq ft attic at R-49 using blown cellulose (R-3.7/in), you need about 13.2 inches of depth. That is approximately 1,100 cu ft settled, needing roughly 134 standard 25 lb bags. Always check the coverage chart on your specific product — coverage varies by brand.
Blown-in cellulose delivers approximately R-3.7 per inch (settled). Blown-in fiberglass delivers approximately R-2.5 per inch (settled). Cellulose achieves higher R-value per inch and also has a slight air-sealing benefit due to its dense packing.
A standard pallet typically contains 25–40 bags depending on the manufacturer and bag weight (25 lb or 30 lb). Check with your retailer for the exact pallet count when ordering in bulk.
Yes. Blown-in insulation requires a blower (also called an insulation blowing machine). Many home improvement retailers offer free or low-cost rental of a blower when you purchase a minimum number of bags. Always follow the manufacturer's instructions for hose length and air pressure settings.
Yes — air sealing first is essential. Seal around recessed lights, plumbing and wiring penetrations, the attic hatch, and any gaps in the top plates before adding insulation. Skipping air sealing significantly reduces the effective performance of added insulation.