Insulation Calculator

How to Calculate Insulation for Walls, Attics & Crawl Spaces

Proper insulation is one of the best investments you can make in a home. The right R-value keeps heating and cooling costs low, improves comfort, and can even reduce noise. Whether you're insulating new construction stud bays, blowing insulation into an attic, or spraying closed-cell foam in a crawl space, accurate material takeoffs prevent waste and extra trips to the supply house.

R-Value Recommendations by Climate Zone

• Zones 1–2 (Hot/Humid — FL, TX coast): Walls R-13, Attic R-30 to R-38
• Zone 3 (Warm — SE states): Walls R-13 to R-15, Attic R-30 to R-38
• Zone 4 (Mixed — Mid-Atlantic): Walls R-13 to R-15, Attic R-38 to R-49
• Zones 5–7 (Cold — Northern US): Walls R-19 to R-21, Attic R-49 to R-60

Insulation Types Compared

• Fiberglass batts: Most common, easy to install, R-3.2 per inch. Comes in pre-cut widths (15" or 23") to fit standard stud spacing.
• Blown-in (cellulose or fiberglass): Great for attics and retrofits. R-3.5 per inch for cellulose. Fills gaps better than batts.
• Spray foam (closed-cell): R-6.5 per inch, doubles as air/moisture barrier. Higher cost but superior performance.
• Spray foam (open-cell): R-3.7 per inch, good for sound and air sealing. Less expensive than closed-cell.

Vapor Barriers & Code Minimums

Most building codes require a vapor retarder on the warm side of insulation in cold climates. Kraft-faced batts include an integrated vapor retarder. In hot/humid climates, the vapor barrier goes on the exterior side. Always check your local building code for minimum R-value requirements — the 2021 IECC has significantly increased minimums in most climate zones.

Coverage Per Bag (Common Products)

• R-13 fiberglass batt (15" wide): ~88.6 sq ft per bag
• R-19 fiberglass batt (15" wide): ~75.1 sq ft per bag
• R-30 fiberglass batt (16" wide): ~58.7 sq ft per bag
• R-38 fiberglass batt (24" wide): ~48 sq ft per bag
• Blown-in cellulose: ~40 sq ft per bag at R-30 (varies by depth)