Calculate exactly how many bags of blown in insulation you need, the required thickness, and estimated cost. Covers both fiberglass and cellulose blown insulation for attics and walls.
Choose your material type, then enter your dimensions.
Blown in insulation (also called blown-in insulation or loose-fill insulation) is a type of insulation that is installed using a blowing machine to fill cavities, attics, and wall spaces. Unlike batts or rolls that come in pre-cut sheets, blown insulation is made up of small particles that are literally blown into place, filling every gap, crack, and hard-to-reach area for superior coverage.
There are two main types of blown in insulation materials:
Cellulose blown in insulation is made from recycled paper products (mostly newspapers) treated with fire-retardant chemicals. It has an R-value of approximately R-3.5 per inch, making it one of the most efficient loose-fill options. Blown in cellulose is especially popular for attic insulation because it fills around obstacles like pipes, wires, and joists more completely than other types.
Fiberglass blown in insulation is made from tiny glass fibers and has an R-value of approximately R-2.5 per inch. While it requires more thickness to achieve the same R-value as cellulose, blown in fiberglass insulation is lighter, does not absorb moisture, and is less prone to settling over time. It is a popular choice for both attics and blown in insulation walls applications.
Our blown in insulation calculator helps you determine exactly how many bags you need, the required installation thickness, and the estimated blown in insulation cost for your project — whether you are insulating an attic, walls, or crawl space.
Figuring out how to calculate blown in insulation is straightforward when you break it into steps. Our blow in insulation calculator automates this process, but here is the math behind it:
Measure the length and width of the area you want to insulate. Multiply them together to get the total square footage.
Divide your target R-value by the R-value per inch of your chosen material. This tells you how thick the insulation needs to be.
For example, to achieve R-49 with cellulose blown in insulation (R-3.5/inch): 49 ÷ 3.5 = 14 inches. With fiberglass blown in insulation (R-2.5/inch): 49 ÷ 2.5 = 19.6 inches.
Each bag of blown in insulation covers a specific area at a given R-value. Divide your square footage by the coverage per bag:
The blown in insulation cost depends on the material and your area. Multiply your square footage by the insulation cost per square foot:
| Material | R-Value/Inch | Cost per Sq Ft | Cost per Bag | Coverage at R-49 |
|---|---|---|---|---|
| Cellulose Blown In | R-3.5 | $0.80 – $1.50 | ~$12 – $15 | ~11 sq ft |
| Fiberglass Blown In | R-2.5 | $0.70 – $1.30 | ~$15 – $20 | ~15 sq ft |
Blown in attic insulation is the most common application. You need to know how much insulation in attic spaces is required based on your climate zone. For blown attic insulation projects, simply measure your attic floor area, choose your R-value based on your climate, and use our calculator. Most attic insulation projects use R-30 to R-60, with R-49 being the most common recommendation for cold climates. Our attic insulation cost calculator estimates the total material cost based on your specific dimensions.
Installing blown in wall insulation (also called blown in insulation walls) requires a different approach than attics. For existing walls, small holes are drilled at the top of each wall cavity, and insulation is dense-packed to fill the entire space. For new construction, insulation can be blown behind netting attached to the studs. Wall insulation typically requires R-13 to R-21 depending on your climate zone. A blown-in insulation calculator for walls accounts for standard stud spacing (16" or 24" on center) and the reduced cavity depth.
Understanding blown in insulation cost helps you budget accurately. Here is a complete breakdown of insulation cost per square foot for blown in materials:
| Project Type | Material Cost/Sq Ft | With Installation | 1,000 Sq Ft Total |
|---|---|---|---|
| Cellulose - Attic (DIY) | $0.80 – $1.20 | N/A (DIY) | $800 – $1,200 |
| Cellulose - Attic (Pro) | $0.80 – $1.20 | $1.50 – $2.50 | $1,500 – $2,500 |
| Fiberglass - Attic (DIY) | $0.70 – $1.00 | N/A (DIY) | $700 – $1,000 |
| Fiberglass - Attic (Pro) | $0.70 – $1.00 | $1.30 – $2.30 | $1,300 – $2,300 |
| Wall Dense-Pack (Pro only) | $1.00 – $1.50 | $2.00 – $3.50 | $2,000 – $3,500 |
The blown in insulation cost per square foot varies based on your location, the contractor you choose, and whether you need to remove existing insulation first. How much does it cost to insulate an attic with blown in insulation? For a typical 1,000 sq ft attic, DIY material cost is $700-$1,200, while professional installation runs $1,300-$2,500 total.
The blown in insulation R-value you need depends on where you live and what part of the house you are insulating. Here is a quick guide:
| Location | Recommended R-Value | Cellulose Thickness | Fiberglass Thickness |
|---|---|---|---|
| Interior Walls (R-11) | R-11 | 3.1 inches | 4.4 inches |
| Exterior Walls (R-13) | R-13 | 3.7 inches | 5.2 inches |
| Floors / Crawl Space | R-19 to R-25 | 5.4 – 7.1 inches | 7.6 – 10 inches |
| Attic - Southern US | R-30 to R-49 | 8.6 – 14 inches | 12 – 19.6 inches |
| Attic - Central US | R-38 to R-60 | 10.9 – 17.1 inches | 15.2 – 24 inches |
| Attic - Northern US | R-49 to R-60 | 14 – 17.1 inches | 19.6 – 24 inches |
The difference between R-11 and R-13 insulation comes down to thickness and performance. R-11 vs R-13: R-11 is about 3.5 inches thick (fits a 2×4 wall cavity) and is suitable for interior walls in mild climates. R-13 is about 3.7 inches thick and provides 18% better thermal resistance. Most building codes require a minimum of R-13 for exterior walls, making R-13 the standard choice for most new construction insulation projects.
DIY blown in insulation is one of the most accessible home improvement projects. If you are considering a do it yourself blown in insulation project, here is what you need to know:
An insulation blowing machine (free rental with bag purchase at most stores), safety gear (mask, goggles, gloves, long sleeves), a helper to feed bags into the machine while you direct the hose, and a ruler or depth gauge to check thickness as you go.
Attic floors are the easiest DIY blow in insulation project. You simply point the hose and fill to the desired depth. Start from the farthest point from the attic access and work your way back. Blow in insulation DIY for open attic spaces typically takes 2-4 hours for a 1,000 sq ft area with two people.
Blown in insulation walls and blown in wall insulation dense-pack projects should be done by professionals. Wall insulation requires drilling precise holes, using specialized dense-pack adapters, and ensuring complete cavity fill without voids — skills that take experience to master.
Choosing between fiberglass blown in insulation and cellulose blown in insulation depends on your specific project. Here is a detailed comparison:
| Feature | Cellulose | Fiberglass |
|---|---|---|
| R-Value per Inch | R-3.5 (higher) | R-2.5 |
| Material | Recycled paper + fire retardant | Glass fibers |
| Cost per Sq Ft | $0.80 – $1.50 | $0.70 – $1.30 |
| Moisture Resistance | Can absorb moisture | Does not absorb |
| Settling Over Time | Settles 15-20% | Minimal settling |
| Air Sealing | Excellent | Good |
| Fire Resistance | Treated (Class 1) | Naturally non-combustible |
| Best For | Attics, existing walls | Walls, humid areas |
| Eco-Friendly | 85% recycled content | 20-30% recycled |
For most blown in attic insulation projects, cellulose is the better choice due to its higher R-value per inch and superior air sealing. For blown in insulation walls in humid climates, fiberglass is preferred because it does not absorb moisture. Use our blown in insulation calculator to compare exact quantities and costs for both materials side by side.
Need a different insulation calculation? Try our other free tools: