Insulation Calculator
Calculate how much insulation you need for walls, attics, and floors. Get estimates for fiberglass batts, blown-in, and spray foam by R-value.
Area Type
Dimensions
Stud / Joist Spacing
Desired R-Value
Insulation Type
Your Results Will Appear Here
Enter your area dimensions and insulation preferences, then click “Calculate” to see how much insulation you need.
Top-Rated Insulation Products
Hand-picked products to help you get the best results on your project.
Owens Corning
Owens Corning R-19 Fiberglass Insulation, 75.07 sq ft
- ✓R-19 rated
- ✓Pre-cut for 2x6 walls
- ✓EcoTouch technology
Greenfiber
Greenfiber Blown-In Cellulose Insulation, 19 lb Bag
- ✓Recycled content
- ✓Fire retardant
- ✓Pest resistant
Frost King
Frost King Fiberglass Insulation Roll, R-3.7
- ✓Easy DIY install
- ✓Flexible roll
- ✓Foil faced
Simpson Strong-Tie
Insulation Support Wires, 100 Pack
- ✓Spring-loaded
- ✓16" and 24" spacing
- ✓Friction fit
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How to Use This Insulation Calculator
Step 1: Choose Area Type
Select whether you’re insulating an attic, exterior walls, or floor/crawlspace. This helps determine the right R-value recommendation.
Step 2: Enter Dimensions
Measure the length and width of the area to insulate. For irregularly shaped attics, calculate the total square footage separately.
Step 3: Select R-Value
Choose the R-value based on your climate zone. Higher R-values provide more insulation. Check DOE recommendations for your area.
Step 4: Pick Insulation Type
Choose fiberglass batts for DIY, blown-in for retrofits, or spray foam for the highest performance and air sealing.
Step 5: Get Results
Click Calculate to see coverage needed, bags, costs, and material quantities. Copy or print results for your shopping list.
Understanding R-Values
R-Value by Application
| R-Value | Thickness | Best For | Climate Zone |
|---|---|---|---|
| R-13 | 3.5″ | 2×4 exterior walls | All zones |
| R-19 | 6.25″ | 2×6 walls, floors | Zones 3–8 |
| R-30 | 9.5″ | Attic (mild climate) | Zones 1–3 |
| R-38 | 12″ | Attic (moderate climate) | Zones 4–5 |
| R-49 | 15.5″ | Attic (cold climate) | Zones 6–8 |
Insulation Types Compared
Fiberglass batts are the most popular DIY option, affordable, and widely available. Blown-in cellulose is ideal for attic retrofits and fills irregular spaces well. Spray foam provides the highest R-value per inch plus excellent air sealing, but costs 2–3 times more than other options and typically requires professional installation.
Pro Tips for Insulating
Don’t Compress Insulation — It Reduces R-Value
Fiberglass insulation gets its R-value from trapped air pockets. Compressing it into a tighter space reduces its effectiveness. If your cavity is too shallow, use a lower R-value batt that fits properly.
Wear Protective Gear — Long Sleeves, Mask, Goggles
Fiberglass can irritate skin, eyes, and lungs. Always wear long sleeves, gloves, safety goggles, and an N95 mask. Work in a well-ventilated area and shower afterward.
Seal Air Leaks Before Insulating
Insulation slows heat transfer but doesn’t stop air movement. Before insulating, seal gaps around wires, pipes, recessed lights, and attic bypasses with caulk or expanding foam for maximum energy savings.
Attics Need R-38 to R-60 in Most Climates
The attic is where you lose the most heat. Most US homes benefit from R-38 to R-49 in the attic. In cold climates (zones 6–8), go up to R-60 for maximum energy savings.
Vapor Barrier Goes Toward the Heated Space
In cold climates, the vapor barrier (kraft paper facing on batts) should face the interior of the home. This prevents warm, moist indoor air from condensing inside the wall cavity.
Frequently Asked Questions
R-value depends on your climate zone. For most US homes: R-13 to R-15 for exterior walls, R-30 to R-60 for attics, and R-19 to R-25 for floors over crawlspaces. Cold climates (zones 5–8) need higher R-values. Check the DOE climate zone map for your specific area.
Fiberglass batts are easier for DIY installation and work well in new construction with exposed stud cavities. Blown-in cellulose is better for retrofit projects—it fills irregular spaces and can be installed through small holes in finished walls without removing drywall.
The most practical method is blown-in insulation. A contractor drills 2–3 inch holes between each stud bay (from outside or inside), blows in cellulose or fiberglass, then patches the holes. This avoids removing drywall and is relatively affordable at $1–$2 per square foot.
You can’t technically over-insulate, but there are diminishing returns above R-60 for attics. The bigger concern is moisture management—adding insulation without proper vapor barriers and ventilation can trap moisture and cause mold. Always ensure proper attic ventilation.
In cold climates (zones 5–8), install vapor barriers on the warm side (interior) of exterior walls. In mixed climates (zones 3–4), check local codes. In hot-humid climates (zones 1–2), vapor barriers typically go on the exterior side. Some insulation products include faced barriers.
For a 1,000 sq ft attic at R-38, plan on roughly 30 bags of blown-in insulation, but bag coverage varies by product, so check the coverage chart printed on the bag. For batts, buy about 1,050 sq ft of coverage and divide by the square footage on each package; thicker, higher R-value batts cover less per package.