Thermal Resistance Calculator
Find thermal resistance, heat flow, or temperature difference.
Calculate
Formulas
R = L / (k × A)L = thickness, k = thermal conductivity, A = area
ΔT = P × RTemperature difference from power and thermal resistance
Thermal Resistance
Conductivities (W/m·K): Copper: 385, Aluminum: 237, Steel: 50, Glass: 1.0, Wood: 0.15, Air: 0.025. Critical for electronics cooling and building insulation.
How Thermal Resistance Works
Thermal resistance measures how strongly a material opposes the flow of heat through it — the thermal analogue of electrical resistance. It depends on thickness, conductivity, and area:
R = L / (k × A)R is thermal resistance (K/W), L is the material thickness, k is thermal conductivity (W/m·K), and A is the cross-sectional area.
A thicker or lower-conductivity material has higher resistance and lets less heat through. Heat flow is then Q = ΔT / R, directly mirroring Ohm's law.
Worked Example
A 0.1 m thick foam panel (k = 0.03 W/m·K) over 5 m²:
R = 0.1 / (0.03 × 5) = 0.667 K/W
With a 20 K temperature difference, heat flow = 20 / 0.667 = 30 W.
Thermal Conductivity Reference
| Material | k (W/m·K) | Role |
|---|---|---|
| Copper | 400 | Conductor |
| Steel | 50 | Conductor |
| Glass | 1.0 | Moderate |
| Wood | 0.15 | Insulator |
| Foam insulation | 0.03 | Insulator |
Frequently Asked Questions
How does this relate to R-value?
Building R-value is thermal resistance per unit area (R = L/k). Higher R-value means better insulation. This calculator includes area for total resistance.
Can thermal resistances be added?
Yes. Layers in series add their resistances, just like series electrical resistors, which is how multi-layer walls are analysed.
What is the electrical analogy?
Temperature difference is like voltage, heat flow like current, and thermal resistance like electrical resistance: Q = ΔT / R.