How to use the thermal resistance calculator
Combine layers to find total R-value and U-value. Enter layer 1 thickness, layer 1 conductivity, layer 2 thickness, layer 2 conductivity in the fields above; the total resistance, u-value, r-value (imperial) are computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- d1 — Layer 1 thickness (m)
- k1 — Layer 1 conductivity (W/(m·K))
- d2 — Layer 2 thickness (m)
- k2 — Layer 2 conductivity (W/(m·K))
Worked example
With layer 1 thickness = 0.1 m, layer 1 conductivity = 0.04 W/(m·K), layer 2 thickness = 0.2 m, layer 2 conductivity = 0.8 W/(m·K), the calculator gives total resistance ≈ 2.75 m²·K/W; u-value ≈ 0.3636364 W/(m²·K); r-value (imperial) ≈ 15.6145 ft²·°F·h/BTU.
Frequently asked questions
What is the formula for the thermal resistance calculation?
Total resistance (m²·K/W) = d1 / k1+d2 / k2. U-value (W/(m²·K)) = 1 / [Total resistance]. R-value (imperial) (ft²·°F·h/BTU) = [Total resistance] × 5.678. Here d1 is layer 1 thickness (m), k1 is layer 1 conductivity (W/(m·K)), d2 is layer 2 thickness (m), k2 is layer 2 conductivity (W/(m·K)).
What inputs do I need for the thermal resistance (r-value) calculator?
You need layer 1 thickness in m, layer 1 conductivity in W/(m·K), layer 2 thickness in m, layer 2 conductivity in W/(m·K). Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use this calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.