Insulation R Value Calculator
Estimate layered insulation resistance.
Calculate insulation r value calculator from clear inputs
Insulation R Value Calculator gives a focused worksheet for home & diy questions where a quick deterministic estimate is more useful than a spreadsheet. The insulation r value calculator fields mirror the variables in its formula, and the output separates the main result from supporting values so you can sanity-check this calculation before reusing it.
Existing R-13 plus 5.5 inches at R-3.2 per inch gives total R-30.6.
Keep the estimate private in your browser
For Insulation R Value Calculator, every calculation runs in your browser with no upload, account, cookie, live lookup, or server-side storage. The insulation r value calculator result is best treated as a planning number because the real-world constraints behind this estimate can change the answer. Adjust the insulation r value calculator assumptions and confirm important decisions against the relevant source of truth for that exact situation.
Frequently Asked Questions
How is the total R-value calculated?
Added R-value = thickness × R per inch, plus the existing R-value. Adding 5.5 inches at R-3.2 per inch to existing R-13 gives R-30.6.
What R per inch should I use?
Roughly R-2.2 to 2.7 for loose-fill fiberglass, R-3.1 to 3.8 for cellulose, around R-3.5 for mineral wool batts, and R-6 to 7 for closed-cell spray foam. Check the product label.
How much attic insulation is recommended?
The US Department of Energy recommends about R-30 to R-60 for attics depending on climate zone. Compressed insulation loses R-value, so do not pack batts into a space thinner than their rated thickness.
Related tools
Browse the full set of free, private, in-browser tools.