Calculate bags of blown-in insulation for attics or walls. Enter area, desired depth, and coverage per bag to estimate material for cellulose or fiberglass loose-fill.
Blown-in (loose-fill) insulation is the most popular choice for attic floors and retrofitting existing walls. It's installed by blowing cellulose or fiberglass fibers through a hose into the space using a blowing machine. The material fills gaps, conforms around obstacles, and creates a continuous thermal barrier without the gaps common in batt installations.
This blown-in insulation calculator estimates the number of bags needed based on your area, desired depth, and the coverage rate per bag. Cellulose insulation (made from recycled paper) and fiberglass loose-fill have different densities and coverage rates, so the calculator accounts for your chosen material.
Most big-box home improvement stores provide free blowing machine rental with a minimum bag purchase (usually 20+ bags), making blown-in insulation one of the most cost-effective DIY insulation projects.
Accurate calculation of this value helps construction professionals plan projects more effectively, reduce material waste, and ensure compliance with building codes and industry standards.
Blown insulation coverage per bag varies by manufacturer, material type, and desired depth. This calculator gives you an accurate bag count so you meet the minimum for free machine rental and don't run short mid-project. Having precise numbers at hand streamlines project planning discussions with clients, architects, and subcontractors, building trust and reducing costly misunderstandings on the job.
Cubic Feet = Area × Depth (inches) ÷ 12 Bags = ⌈(Area × (1 + Waste%)) ÷ Coverage per Bag⌉
Result: 32 bags
1,200 sq ft attic at 14" depth with 5% waste = 1,260 sq ft effective area. At 40 sq ft coverage per bag at that depth: 1,260 ÷ 40 = 31.5 → 32 bags of blown cellulose insulation.
Every bag of blown insulation has a coverage chart on the label showing square feet per bag at different depths. As depth increases, coverage per bag decreases because more material is used per square foot. Always use the coverage rate for your specific target depth.
Start at the far end of the attic and work toward the access opening. Keep the hose at a consistent height and move steadily to build even depth. Use depth markers (ruler stakes) every 4–6 feet to check uniformity.
Wall retroits use dense-pack technique: drill 2–3 inch holes between studs, insert the insulation hose, and blow cellulose at high density (3.5 lbs/cu ft). This fills every void and air-seals the wall simultaneously.
Blown cellulose costs about $0.30–$0.50 per sq ft for DIY attic installation (material only). Professional installation runs $1.00–$2.00 per sq ft. Properly insulating an under-insulated attic can save 10–30% on heating and cooling costs.
Cellulose (recycled paper) is denser, cheaper, and has a higher R-value per inch (R-3.5–R-3.8 vs R-2.2–R-2.7 for loose fiberglass). Fiberglass is lighter and doesn't absorb moisture. Cellulose is the more popular choice for attics.
It depends on depth. For R-49 cellulose (about 14" depth): approximately 25–30 bags per 1,000 sq ft. For R-38 (about 10.5"): approximately 18–22 bags. Check the specific product's coverage chart.
Yes, through holes drilled in the exterior siding or interior drywall. Dense-pack cellulose at 3.5 lbs/cu ft is the standard technique for wall retrofits. This requires different machine settings than attic blowing.
Fiberglass settles 10–20% over time unless installed at the proper density. Cellulose settles about 15–20% in attics. Manufacturers account for settlement in their coverage charts — the "installed" depth is higher than the "settled" depth.
Usually not. Blown-in insulation can be added on top of existing batts or loose-fill. The R-values are additive. However, remove old insulation if it's water-damaged, pest-contaminated, or if you need to air-seal first.
Yes, most Home Depot and Lowe's locations offer free 24-hour blowing machine rental with a minimum insulation purchase (typically 20+ bags). The machine, hose, and basic instructions are included.
A typical 1,000–1,500 sq ft attic takes 2–4 hours with two people (one feeding bags into the machine, one directing the hose). Plan a full day including setup, insulating, and cleanup.
Modern cellulose is treated with borate fire retardant and is fire-safe. Fiberglass particles can irritate skin and lungs. Wear a dust mask, goggles, and long sleeves during installation regardless of material type.