INSULATION
INSULATION BATTS
batts = wall area ÷ batt sf
ft
ft
RESULT
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Standard R-13 batt covers 32 ft² (16" OC, 8 ft tall). Subtract ~10% for studs/openings for net.
About this calculator
This insulation calculator estimates the number of fiberglass or mineral wool batts you need for walls or ceilings. R-13 batts (for standard 2x4 walls with 16-inch-on-center studs) cover 32 ft² each in a typical 8-foot-tall wall. R-19 (for 2x6 walls) and R-30/R-38 (for ceilings) cover less per batt because they are wider or taller. Subtract 10% for studs, doors, and windows if you want net insulation; the calculator gives gross batts.
Common questions
What R-value do I need?
Depends on climate zone and where you're insulating. Walls: R-13 (2×4) or R-19/R-21 (2×6). Attic: R-38 in southern US, R-49 in northern. Basement walls: R-15. Crawl space ceiling: R-19. Check your local code for exact requirements.
Faced or unfaced insulation?
Faced (kraft paper or foil) for walls and ceilings — the facing is a vapor barrier and faces the warm side. Unfaced for layering on top of existing insulation, or where you'll add a separate vapor barrier. Never put two faced layers in one cavity.
How much does insulation cost?
R-13 fiberglass batts: $0.50–0.85/ft² installed yourself, $1.50–2.50/ft² installed pro. Blown cellulose attic: $1–2/ft². Spray foam open-cell: $1.25–2.25/ft²; closed-cell: $1.75–4/ft².