R-Value Calculator
Calculate total R-value for your wall or ceiling assembly
Rigid foam or mineral wool
Plywood/OSB
Fiberglass batts in stud cavity
1/2" drywall
Total R-Value
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Assembly U-Factor
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Meets Code?
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Disclaimer: Results are estimates based on standard formulas. Not a substitute for professional advice from a licensed contractor, engineer, or architect. Verify all calculations before making purchasing or construction decisions.
How to Use This Calculator
Total R-value determines how well your assembly resists heat flow. Our calculator adds up thermal resistance of each layer.
- Identify each material layer
- Enter R-value for each layer
- Calculator sums all R-values
- Compare against climate zone code
Expert Insights
Smart analysis for your Insulation project
R-Value by Climate Zone
Attic: R-30 to R-60 depending on zone. Walls: R-13 to R-20+. AI maps your region to DOE climate zone recommendations.
Air Sealing Impact
Air sealing before insulating improves efficiency 20-40%. AI calculates the combined R-value benefit of sealing + insulating.
Batt vs Blown-In vs Spray Foam
Batts: lowest cost, DIY-friendly. Blown-in: better coverage. Spray foam: air seals + insulates. AI compares cost per R-value for each.
Calculation Formula
Total R = R1 + R2 + R3 + ... (sum of all layers)
U-Factor = 1 / Total R
Authority References
Our calculations are based on guidelines and standards from these authoritative sources:
- U.S. Department of Energy (DOE) — Insulation R-Value Recommendations by Climate Zone. Learn more
- ENERGY STAR — Recommended Home Insulation R-Values. Learn more
- International Energy Conservation Code (IECC) — Climate Zone Insulation Requirements. Learn more
Frequently Asked Questions
What R-value is required by code?
IRC 2021: Walls R-20 or R-13+5ci, Ceilings R-49, Floors R-19, Basements R-15 continuous or R-19 cavity.
What is a U-factor?
U-factor measures heat transfer rate - lower is better. U = 1/R. Codes specify maximum U-factors.