Insulation Calculator
Calculate batts, rolls, or bags of blown-in insulation for your project.
Results
Total Area —
Quantity —
R-Value —
Estimates include 5% waste. Check local building codes for minimum R-value requirements.
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How to Calculate Insulation
Insulation is measured by R-value (thermal resistance). Higher R-values mean better insulation. The amount you need depends on the area, insulation type, and your climate zone.
Insulation Formula
Total Area = Length × Height (in sq ft)
For batts: Bags = Area / Coverage per bag (check packaging)
For blown-in: Bags = Area × Depth / Coverage per bag
For batts: Bags = Area / Coverage per bag (check packaging)
For blown-in: Bags = Area × Depth / Coverage per bag
Recommended R-Values by Climate Zone
- Zone 1-2 (Hot): Walls R-13, Attic R-30 to R-49
- Zone 3 (Warm): Walls R-13 to R-15, Attic R-30 to R-60
- Zone 4 (Mixed): Walls R-13 to R-21, Attic R-38 to R-60
- Zone 5-6 (Cold): Walls R-20 to R-21, Attic R-49 to R-60
- Zone 7-8 (Very Cold): Walls R-21+, Attic R-49 to R-60
Insulation Types Compared
- Fiberglass batts: Most common, affordable, DIY-friendly. R-3.1 to R-3.4 per inch.
- Blown-in cellulose: Good for attics and retrofits. R-3.2 to R-3.8 per inch. Requires blower machine.
- Blown-in fiberglass: Lighter than cellulose, won't absorb moisture. R-2.2 to R-2.7 per inch.
- Rigid foam (XPS/EPS): Great for basements, exterior walls. R-5 per inch (XPS).
- Spray foam: Best R-value per inch (R-6 to R-7 closed-cell), but most expensive. Professional install required.
Installation Tips
- Don't compress fiberglass batts — compression reduces R-value
- Use unfaced insulation when adding to existing insulation
- Vapor barrier goes on the warm side (toward heated space)
- Wear protective equipment: long sleeves, gloves, mask, and safety glasses
- Don't cover soffit vents — attics need ventilation to prevent moisture problems
An insulation stapler speeds up batt installation in stud cavities. Browse insulation at Lowe's to compare R-values and pricing for your project.