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R Value Calculator
Quick answer: For layers stacked in a row, the total R-value is the sum of each layer's thickness multiplied by its R per inch. Enter up to three layers. The answer is a nominal value; framing, gaps, compression, moisture and air leaks reduce real-world performance, so treat the total as a best case, not a guarantee.
How it works
Total R = Σ (thickness × R per inch). R-values in series add because heat must pass through each layer. Parallel paths, such as wood studs between batts, do not simply add, which is why whole-wall R is lower than cavity R. Use typical R per inch from the R-value chart or, better, the product's label. Compare the total with ENERGY STAR recommended levels or your Canadian code via Canada R-value requirements.
Worked example
Figures below are illustrative examples (2026-10-29), not quotes or guarantees.
Assumptions: 3.5 in fiberglass batt at an assumed R3.2/in plus 1 in rigid foam at an assumed R5/in. Total = 11.2 + 5 = R16.2 nominal.
FAQ
Does doubling thickness double R?
Roughly, for the same material, if it is not compressed.
What about air gaps?
Small air spaces add little; air leaks reduce performance. See air sealing first.
Is R the same as U?
U is roughly 1 ÷ total R for an assembly, including films and framing.
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