Construction Calculators

Insulation Calculator

Estimate how many fiberglass batts you need for a wall or attic, based on standard 16" or 24" on-center framing. Includes recommended R-values by climate zone from ENERGY STAR / the 2021 IECC.

Inputs

Batts needed

Fill the form and press Calculate.

Recommended R-values by climate zone

Batt count here is pure geometry (area ÷ coverage per batt). How much R-value you actually need depends on where the wall or attic is. The table below is ENERGY STAR's published guidance, based on the 2021 International Energy Conservation Code (IECC) Table R402.1.3.

U.S. IECC climate zones 1 (warmest) through 8 (coldest). Canadian builds should confirm against the National Building Code / local energy code — it sets its own zone map and can call for more than a U.S. zone of similar latitude.
Assembly	Zone 1–3	Zone 4	Zone 5–8
Attic (uninsulated)	R30–R49	R49–R60	R49–R60
Attic (existing 3–4")	R25–R49	R49	R49
Floor over unheated space	R13–R25	R30	R30–R38
Wall sheathing (re-siding)	R5 (zone 3 only)	R5–R10	R5–R10
Basement/crawlspace wall	R5 sheathing or R13 batt	R10 sheathing or R13 batt	R15 sheathing or R19 batt

Batt size varies by manufacturer and package. The 93" length above is typical for an 8 ft wall; adjust it to match the batts you're buying before you order.