Insulation Thickness (R-Value) Calculator

About this calculator

R-value measures a material's resistance to heat flow, and it's additive with thickness — thickness = target R-value ÷ R-per-inch for the specific material. Different insulation types pack very different R-value per inch: closed-cell spray foam runs around R-6 to R-6.5/inch, fiberglass batts about R-3 to R-3.2/inch, and loose-fill cellulose around R-3.5/inch, so the same target R-value calls for very different thicknesses depending on material.

Builders and energy auditors use this to plan attic, wall, and floor insulation thick enough to meet local building code minimums (commonly R-38 to R-60 for attics in colder climates), and homeowners comparing insulation products use it to see how much cheaper, bulkier material they'd need versus a thinner, pricier option to hit the same performance.