Quantity · Cellulose insulation
Cellulose Insulation Calculator
Size cellulose two ways: open-attic settled bags from an R gap, or dense-pack walls from cavity volume × density (lb/ft³). Fiberglass comparison charts live on the blown-in calculator; this page stays cellulose-only — including closed-cavity packing the blown-in tool skips.
Cellulose details
Uses settled bag coverage by R — same family as blown-in, cellulose only.
Bags to buy
41bags
Add R-30 · 8.3 in settled
- Settled depth
- 8.3 in
- Coverage
- 26 sq ft/bag
- Weight
- ~1,010 lb
- Rough installed
- $1,200–$2,300
~26 sq ft/bag at R-30 settled · ~1010 lb (25 lb bags)
- R to blow = target − existing
- Settled inches + sq ft/bag from cellulose attic chart
- Bags from coverage, then × bag weight for total lb
Price data updated . National US ranges from published supplier and contractor averages. Not a bid. Local quotes vary.
How cellulose bag counts are calculated
Open attic follows a settled bag chart for the R you still need. Dense-pack ignores that chart: cubic feet of cavity times target density gives pounds, then pounds divide by bag weight (typically 25 lb).
// Open attic r_needed = max(0, r_target − r_existing) bags = ceil(area ÷ sq_ft_per_bag(r_needed) × (1 + waste %)) // Dense-pack walls volume_cf = area_sq_ft × cavity_depth_in ÷ 12 pounds = volume_cf × density_pcf × (1 + waste %) bags = ceil(pounds ÷ bag_weight_lb)
Worked example. Open attic: 1,000 sq ft from R-19 to R-49 needs R-30 → about 8.3 in settled cellulose and ~38–39 bags before overblow (~41 bags at 5% waste, ~1,025 lb). Dense-pack: 1,000 sq ft of 3.5" 2×4 walls at 3.5 lb/ft³ is 291.7 cu ft → ~1,021 lb before waste → about 43 × 25 lb bags at 5% waste.
Cellulose density by application (lb/ft³)
Density is why attic bag charts and wall packing are different math. Use the open-attic mode for settled loose-fill; switch to dense-pack and set lb/ft³ for closed cavities.
| Application | Density lb/ft³ | Typical | Use |
|---|---|---|---|
| Open attic (settled) | 1.4–1.8 | 1.5 | Loose-fill after settle |
| Open attic (as-blown) | 1.6–2.0 | 1.8 | Machine setting before settle |
| Dense-pack wall | 3.5–4.0 | 3.5 | Closed stud cavities |
| Floor / cathedral pack | 3.0–3.5 | 3.2 | Horizontal / sloped bays |
- Dense-pack must stay in a closed, netted, or drilled cavity — dumping attic-density fiber into walls settles and voids.
- Bag weight here assumes 25 lb cellulose bags; check your brand.
Open-attic cellulose bags per 1,000 sq ft (settled R)
Cellulose-only settled chart before overblow for a full blown layer (existing = 0). Top-ups use the R gap. Compare fiberglass side-by-side on the blown-in calculator.
| Settled R | Inches | Sq ft / bag | Bags / 1,000 | ≈ lb / 1,000 |
|---|---|---|---|---|
| R-19 | 5.5" | 41 | 24 | 600 |
| R-30 | 8.3" | 26 | 38 | 950 |
| R-38 | 10.4" | 21 | 48 | 1,200 |
| R-49 | 13.3" | 16 | 63 | 1,575 |
| R-60 | 16.3" | 13 | 77 | 1,925 |
Cellulose Insulation calculator FAQ
- How many bags of cellulose insulation do I need?
- For an open attic, find the R gap and divide area by the settled sq ft per bag on the cellulose chart, then add a little overblow. For dense-pack walls, multiply cavity volume by density to get pounds and divide by bag weight (often 25 lb).
- What is dense-pack cellulose?
- Dense-pack blows cellulose into a closed cavity at roughly 3.5–4.0 lb/ft³ so the fiber stays put and air-seals better than light attic fill. It needs nets, retarder, or drilled holes — not an open joist bay.
- Why is this separate from the blown-in calculator?
- Blown-in compares fiberglass vs cellulose on open-attic bag charts only. This page is cellulose-focused and adds density-based dense-pack math for walls and closed cavities.
- Can I use attic bag charts for walls?
- No. Attic settled coverage assumes light density. Walls need the dense-pack mode (volume × lb/ft³) or the fiber will settle and leave voids.
- Is the dollar range a bid?
- No — it is a rough installed band from national cellulose price rows. Access, air sealing, and dense-pack labor vary. For attic job add-ons, use the attic insulation cost calculator.
- What bag weight should I assume?
- This tool uses 25 lb bags, a common US DIY size. If your brand is 22.5 or 30 lb, scale bags by weight or check the coverage chart printed on the bag.
Related tools
Blown-in calculator (FG vs cellulose) · Attic insulation calculator (depth → R) · Attic insulation cost calculator · All insulation calculators