R-Value Calculator
Pick your insulation and thickness. See if it meets your climate's target.
100% in your browser - no upload, no sign-up.
Assembly R-value
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R per inch
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Recommended R
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✅ Meets or beats the recommended R for this assembly and climate zone.
⚠️ Close, but a bit under the recommended R - consider more thickness or a higher-R material.
⛔ Well below the recommended R - add thickness or switch to a higher-R material.
💡 These are planning numbers. Cavity depth, framing thermal bridging and air-sealing all affect real performance, and code minimums vary by jurisdiction. Confirm your local energy code - and remember air-sealing often matters as much as R-value.
⚠️ Enter the cavity depth - a squashed batt loses its R-value.
How to use this R-value calculator
- Pick your insulation material - each has a different R-value per inch.
- Enter the installed thickness in inches (the cavity depth or board thickness).
- Choose the assembly and your climate zone to see the recommended R and how yours compares.
How R-value is calculated
R-value measures resistance to heat flow - the higher the number, the better the insulation. The assembly R-value is simply the material's R-value per inch times its installed thickness: 6 inches of fiberglass batt at R-3.2 per inch gives about R-19. Materials differ widely - fiberglass is about R-2.5 to R-3.2 per inch, cellulose R-3.5, mineral wool R-4, and rigid foams from R-4 (EPS) up to R-6.5 (closed-cell spray). The recommended totals follow Energy Star and IECC guidance, which set higher R-values for colder climate zones - an attic wants about R-30 in zone 1 and R-60 in zones 4 through 7. Layers add: two materials in series sum their R-values.
Frequently asked questions
- How much insulation do I need?
- It depends on the assembly and your climate zone. Energy Star recommends roughly R-30 to R-60 for attics, R-13 to R-21 for walls and R-13 to R-38 for floors, with the higher numbers in colder zones. Pick your material, thickness, assembly and zone above and the calculator shows the recommended R and whether you've hit it.
- How thick is R-19 or R-30 insulation?
- Divide the target R-value by the material's R per inch. R-19 in fiberglass batt (about R-3.2 per inch) is roughly 6 inches; R-30 is about 9 to 10 inches. A higher-R material reaches the same R-value in less thickness - R-30 in closed-cell spray foam (R-6.5) is under 5 inches. Enter a thickness above to see the R-value it produces.
- What is a good R-value for exterior walls?
- Most codes call for about R-13 to R-15 in a 2×4 wall and R-19 to R-21 in a 2×6 wall, rising toward R-20-plus with continuous exterior insulation in colder zones. Because a 2×4 cavity limits you to about R-15, colder climates often add rigid foam sheathing outside the studs. Choose Wall and your zone above for the recommended target.
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