Insulation Calculator

Enter your room dimensions and what you're insulating. We'll size the order — batts, rolls, or bags of blown-in.

Length (ft) Width (ft) Wall height (ft) Doors Windows

What are you insulating?

Walls Ceiling / attic floor

Insulation type

Fiberglass batts Rolls Blown-in cellulose Rigid foam board

Advanced options

R-value target Stud spacing (in OC) Batt coverage (sq ft / batt) Roll coverage (sq ft / roll) Blown coverage (sq ft / bag) Rigid panel (sq ft / sheet) Waste factor (%) Cost per unit ($)

Buy 0 batts

R-value guidance R-13 to R-21 walls Standard for 2×4 walls in mild-temperate climates. Bump to R-19+ for 2×6 walls or colder zones.

Wall area: 0 sq ft
Ceiling area: 0 sq ft
Total area: 0 sq ft
With waste factor: 0 sq ft
Estimated cost: —

How the insulation calculator works

For walls, the area is the perimeter 2 × (length + width) × height, minus a standard area per door (20 sq ft / 1.86 m²) and per window (15 sq ft / 1.4 m²). For ceilings/attics, it's length × width. Add a 10% waste factor for trimming and stuffing, then divide by the coverage of your chosen insulation form.

R-value by climate zone (US)

Zone 1–2 (FL, S. TX, S. AZ) — walls R-13, ceilings R-30.
Zone 3 (TN, NM, mid-CA) — walls R-13 to R-15, ceilings R-30 to R-38.
Zone 4 (NC, OR coast, mid-east) — walls R-13 to R-15, ceilings R-38 to R-49.
Zone 5 (Midwest, NY) — walls R-13 to R-21, ceilings R-49.
Zone 6 (MN, WI, ME) — walls R-19 to R-21, ceilings R-49 to R-60.
Zone 7–8 (AK, far north) — walls R-21+, ceilings R-60.

Insulation type tradeoffs

Fiberglass batts — easiest DIY for new construction with exposed studs. Pre-cut to standard stud bays (16" or 24" OC). Cheapest material.
Mineral wool batts — better fire resistance and sound damping than fiberglass. Slightly more expensive.
Blown-in cellulose — best for unfinished attic floors and retrofitting walls (drilled-and-filled). Requires a rented blower or pro install.
Rigid foam board — for exterior insulation, basement walls, or under slabs. Highest R-per-inch.
Spray foam — best air seal but professional install (not in this calculator's scope).

Common questions

How many batts in a bag?

Varies by R-value and bay width. A typical R-13 fiberglass batt for 16" OC walls comes 8 batts per package, covering ~88 sq ft (8.2 m²). For 24" OC, 6 batts per package, ~96 sq ft (8.9 m²). Always check the package label — coverage and R-value are printed clearly.

What about vapor barriers?

In cold climates (Zone 5+), use kraft-faced batts or install a separate poly vapor barrier on the warm-in-winter side (interior). In hot-humid climates (Zone 1–2), the vapor barrier is on the exterior. In mixed zones (Zone 3–4), use unfaced batts and let the wall breathe.

Can I add more batts on top?

Yes for ceilings — laying R-19 perpendicular over existing R-30 brings you to R-49 and is a common upgrade. NOT for walls — compressed insulation loses R-value. Don't stuff R-19 into an R-13 cavity; it won't help.