Choose what you know (R-value or U-value), enter the thermal conductivity λ of the material, and the tool will estimate the required insulation thickness.
Insulation thickness calculator from R-value, U-value and λ
This insulation calculator estimates the required insulation thickness from either a target R-value (thermal resistance) or a target U-value (thermal transmittance), using the material’s thermal conductivity λ (lambda). It is a practical helper for quick building-physics checks when comparing insulation materials (mineral wool, EPS, PIR, wood fiber, etc.). All calculations are performed locally in your browser.
What do R, U and λ mean?
λ (W/m·K) describes how easily heat flows through a material: lower λ generally means better insulation. R (m²·K/W) is the thermal resistance of a layer: higher R generally means better insulation. U (W/m²·K) is the heat transfer coefficient: lower U generally means better insulation performance.
Formulas used in this tool (simplified)
For a single homogeneous insulation layer, the thickness e is computed with: R = e / λ, so e = R × λ. If you start from U, the tool converts it using the simplified relation U ≈ 1 / R (single layer only).
Example calculation
Example: if you target R = 4.0 m²·K/W and your insulation has λ = 0.035 W/m·K, then the estimated thickness is: e = 4.0 × 0.035 = 0.14 m, i.e. about 14 cm.
Important limitations
This calculator provides an indicative thickness for the insulation layer only. It does not include additional layers and effects such as interior/exterior air films, thermal bridges, masonry layers, fasteners, or moisture conditions. For compliance checks, always refer to professional design methods and local regulations.
Tip: choose whether you know R or U, enter λ, then enter only the known value. The tool will compute thickness and show the equivalent U-value for that single insulation layer.