Insulation R-Value Calculator

Add up the R-value of your insulation layers, compare it to the recommended level for your climate, and see how much more to add.

Layers
Pick a material and enter its thickness in inches, or choose “R-value” to type the rating printed on a batt or board.
Climate Zone (for the Attic Goal)
From the DOE / IECC climate zone map. Zone 4 here means 4A or 4B; Marine 4C uses the zone 5 goal.
Where
Fractions and decimals both work.
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Total R-Value
Recommended
Still needed
To reach it, add
Status

Saved Assemblies

Items you add are saved in this browser.

NameLayersTotal RGoalRemove

How R-Value Adds Up

R-value measures how well insulation resists heat flow; higher is better. When layers are stacked, their R-values add. Most insulation is rated per inch, so multiply the R per inch by the thickness.

Total R = R per inch₁ × thickness₁ + R per inch₂ × thickness₂ + …
Thickness needed = (target R − existing R) ÷ R per inch

Worked Example

R-Value per Inch

Typical values from the U.S. Department of Energy; XPS is the rating manufacturers commonly print. Check the product label.

MaterialR per InchInches for R-38Inches for R-49

Recommended R-Values

ENERGY STAR recommendations for adding insulation to existing wood-framed homes, based on the 2021 IECC.

ZoneUninsulated AtticAttic With 3–4″Floor
1R30R25R13
2R49R38R13
3R49R38R19
4A, 4BR60R49R19
4C, 5, 6R60R49R30
7, 8R60R49R38

Tips

Air sealing matters as much as R-value: seal gaps around wiring, plumbing and the attic hatch before adding insulation. Loose-fill settles, so blow it a little deeper than the target and check the bag's chart for settled thickness and coverage. Compressed batts lose R-value, so don't stuff an R-19 batt into a 2×4 wall.