Insulation R-Value Calculator
Find the insulation thickness needed for a target R-value from the material’s R per inch, plus how many bags or batts cover your area. Calculates in your browser.
Thickness needed
-
Show the math
Thickness is the target R-value divided by the material’s R per inch:
thickness = target R ÷ R per inch
bags = ⌈area ÷ coverage per bag⌉
Recommended R-values depend on climate and assembly, attics often target R-38 to R-60. Check your local code or energy program. All math runs locally in your browser.
What this does
An insulation calculator finds the thickness needed for a target R-value from the material’s R per inch, plus how many bags or batts cover your area.
How to use it
- Enter your target R-value.
- Enter the R per inch.
- Enter the area.
- Read the thickness and bags or batts.
How it works
Divide the target R-value by the material’s R per inch. Attics often target R-38 to R-60 depending on climate.
thickness = target R ÷ R per inch
Understanding your result
The thickness hits your target R-value, but real-world performance falls when batts are compressed or gaps are left, so install to the full depth without squashing and seal air leaks first, since air movement defeats insulation. Aim for the R-value your climate zone recommends rather than the minimum, because the extra depth pays back for decades.
Example
R-38 in R-3.2/inch fiberglass needs about 12 inches.
Sources & methodology
Last updated .
Frequently asked questions
What R-value do I need?
It depends on climate and assembly, attics often target R-38 to R-60. Check your local code or energy program for the right value.
How is thickness found?
Divide the target R-value by the material’s R per inch. For example, R-38 in R-3.2/inch fiberglass needs about 12 inches.
Which material is best?
Closed-cell spray foam has the highest R per inch; batts and blown fiberglass are cheaper per R. The tool lets you set the R per inch.
Is anything stored?
No. Everything is calculated locally in your browser.
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