About & methodology

Insulation Calculator is a free tool that tells you how much insulation your home needs, based on where you live. No sign-up, no email wall — the numbers are computed in your browser.

From ZIP to climate zone

Insulation recommendations are set by IECC climate zone, which is defined at the county level. We map your ZIP code to its county and zone using two public datasets: the DOE / ORNL IECC climate-zone-by-county table and a Census-derived ZIP-to-county crosswalk — covering roughly 32,000 U.S. ZIP codes.

Recommended R-values

For your zone we show the U.S. DOE / ENERGY STAR recommended R-values (aligned with the 2021 IECC) for the attic, exterior walls, floors, and crawlspace/basement. These are recommended levels, given as a range where the sources publish one.

Thickness, cost, and savings

• Thickness = target R-value ÷ the material's R-per-inch (typical published values).
• Cost scales with area × R-value, with a labor multiplier for a professionally-installed range — a planning estimate, not a quote.
• Savings use the standard conductive heat-loss model (area × ΔU × heating degree-days), modeling heating only, so the figure is conservative.
• The federal 25C tax credit returns 30% of insulation materials, up to a shared $1,200/year.

Important

These are planning estimates from published models and data — not a substitute for local energy-code requirements, a contractor's quote, or professional tax advice. Confirm code requirements and 25C/rebate eligibility before you buy or file.