Insulation R Value Calculator
insulation r-value calculator. Get instant, accurate results. Enter values for instant results with step-by-step formulas.
Reviewed by Abdullah, Technical Content Specialist
Formula
R = thickness / k-value | Total R = ฮฃR per layer
Higher R-value = better insulation. Required R varies by climate zone (R-13 walls to R-60 attics).
Worked Examples
Example 1: Fiberglass batt
Problem:3.5\" thick, R-3.8/inch
Solution:R = 3.5 ร 3.8 = R-13.3
Result:R-13.3
Example 2: Attic retrofit over existing insulation
Problem:Adding 6\" of blown cellulose (R-3.7/inch) over an existing R-19 attic layer
Solution:New R = 6 ร 3.7 = R-22.2\nTotal R = 22.2 + 19 = R-41.2
Result:R-41.2 total, meets most R-38 to R-49 attic code minimums
Example 3: Closed-cell spray foam wall
Problem:2\" of closed-cell spray foam at R-6.5/inch, no existing insulation
Solution:R = 2 ร 6.5 = R-13.0
Result:R-13.0, equivalent to a standard 3.5\" fiberglass batt in about half the thickness
Frequently Asked Questions
What R-value insulation do I need for my climate zone?
The US has 8 climate zones. Zone 1-2 (hot): R-13 to R-15 walls, R-30 attic. Zone 3-4 (mixed): R-13 to R-21 walls, R-38 attic. Zone 5-8 (cold): R-20 to R-21 walls, R-49 to R-60 attic. Higher R-values mean better thermal resistance and energy savings.
References
Reviewed by Abdullah, Technical Content Specialist ยท Editorial policy