R-per-inch & depth for R-38/R-49/R-60

Each insulation material adds a fixed R per inch; depth for a target R is inches = R ÷ R-per-inch. This chart lists the common materials and the depth each needs for the DOE-recommended R-38 to R-60 range. Use the insulation depth calculator for any target.

MaterialR / inchR-38 depthR-49 depthR-60 depth
Fiberglass batt3.211.9 in15.3 in18.8 in
Blown fiberglass2.515.2 in19.6 in24.0 in
Blown cellulose3.510.9 in14.0 in17.1 in
Open-cell foam3.710.3 in13.2 in16.2 in
Closed-cell foam6.55.8 in7.5 in9.2 in

Depth = target R ÷ R-per-inch. DOE recommends about R-38 to R-60 in attics by climate zone.

Related calculators

Insulation DepthFind how many inches of attic insulation you need to hit a target R-value — R-38, R-49 or R-60 — for cellulose, fiberglass batts, blown fiberglass or foam.Assembly R-ValueAdd up the R-value of stacked attic insulation layers. Enter each layer's thickness and material to get the assembly R-value, with a thermal-bridging note.Blown-In BagsWork out how many bags of blown-in attic insulation you need from your floor area and the coverage printed on your bag label at the target R-value.