Insulation Calculator

Insulation Calculator

Batt packages and rolls by R-value for walls, attics, floors, and crawl spaces. R-11 through R-49 coverage.

The Short Answer: A 1,000 sq ft attic insulated to R-38 needs about 24 packages of fiberglass batts (each covering ~42 sq ft). Standard 2×4 wall cavities take R-13 or R-15 batts; 2×6 walls take R-19 or R-21. Always insulate to your local building code minimum.

Insulation Calculator

Total area
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Packages needed
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Coverage per pkg
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Faced rolls
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Coverage per package varies by manufacturer. Estimates based on standard fiberglass batt packaging from major manufacturers (Owens Corning, Johns Manville, CertainTeed).

How to Choose the Right R-Value

R-value measures thermal resistance — higher R means better insulation. The right R-value depends on where the insulation goes and your climate zone. The U.S. Department of Energy publishes recommended R-values by zone and building component.

Batts vs. Blown-In vs. Spray Foam

Fiberglass batts are the most common DIY option — precut to fit standard stud spacing (15" for 16" OC, 23" for 24" OC). This calculator estimates batt quantities. Blown-in insulation (cellulose or fiberglass) is better for attics with irregular framing or existing insulation. Spray foam provides the best air sealing but costs 2-3× more than batts and typically requires professional installation.

How Much Insulation Do I Need?

Measure the total area to insulate in square feet. For walls, that's the wall height × width minus windows and doors. For attics, measure the floor area. Then select the R-value for your application — the calculator returns the number of packages based on standard manufacturer coverage per package.

Frequently Asked Questions

At R-38 (recommended for most cold climates), you'll need about 24 packages of fiberglass batts — each package covers approximately 42 sq ft. At R-30 (moderate climates), about 21 packages at 49 sq ft per package. The calculator above adjusts automatically by R-value.

Yes — layering unfaced batts over existing insulation is one of the most cost-effective energy upgrades. Use unfaced (no vapor barrier) batts placed perpendicular to the existing layer. If the existing insulation is R-19 and you add R-19 on top, you get approximately R-38 total. Do not compress the existing insulation — compression reduces R-value.

Faced insulation has a kraft paper or foil vapor barrier on one side. Use faced batts on exterior walls with the facing toward the heated interior (warm-in-winter side). Use unfaced batts when adding to existing insulation, in interior walls for soundproofing, or when a separate vapor barrier is being installed.

The Bottom Line

Insulation is the single most impactful energy efficiency upgrade for most homes. The payback period for attic insulation is typically 1-3 years in heating-dominated climates. Measure your area, select the R-value your climate zone requires, and let this calculator tell you how many packages to buy. Wear long sleeves, gloves, a dust mask, and eye protection — fiberglass batts are no fun to handle without protection.

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