Insulation R-Value Calculator
Estimate the thermal resistance of one or more identical insulation layers from thickness and thermal conductivity, and calculate the corresponding U-value for the material layers.
How to use this calculator
- Enter layer thickness in millimetres, conductivity in W/(m·K) and the number of identical layers.
- Check the labels and units before applying the result to a real task.
- Change one input at a time when comparing scenarios.
Formula and method
R = thickness/λ; U ≈ 1/R for the entered layers
- R = thickness/λ; U ≈ 1/R for the entered layers
- This material-layer calculation excludes framing bridges, surface films, air leakage, moisture, workmanship and other components of a complete assembly.
Worked examples
Worked example
A 100 mm insulation layer with thermal conductivity 0.04 W/(m·K).
R = 0.1/0.04 = 2.5 m²·K/W; the corresponding material-only U estimate is 0.4 W/(m²·K).
R = 0.1/0.04 = 2.5 m²·K/W; the corresponding material-only U estimate is 0.4 W/(m²·K).
Understanding the result
Estimate the thermal resistance of one or more identical insulation layers from thickness and thermal conductivity, and calculate the corresponding U-value for the material layers.
This material-layer calculation excludes framing bridges, surface films, air leakage, moisture, workmanship and other components of a complete assembly.
Important notes
This material-layer calculation excludes framing bridges, surface films, air leakage, moisture, workmanship and other components of a complete assembly.
Displayed values are rounded for readability; retain appropriate precision when continuing a calculation.
Frequently asked questions
Is a higher R-value better insulation?
For the same test basis, a higher thermal resistance means less heat transfer through that layer under the same temperature difference.
Does U-value equal the inverse of R-value?
For this simplified material-only layer, yes. A whole-wall U-value must include all layers, surface resistances and thermal bridges.
Can this determine building compliance?
No. Local requirements and whole-assembly performance need the relevant standards and a correctly defined construction build-up.
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Related explanations
Learn the method behind the number or compare the terminology before using the calculator.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.