What is thermal resistance?

Thermal resistance (R) measures how strongly a material opposes heat flow. Higher R means better insulation. The formula is R = L / (k × A), where L is thickness (m), k is thermal conductivity (W/m·K), and A is cross-sectional area (m²). Unit: K/W.

What is the difference between series and parallel thermal resistance?

In series (layers stacked in the direction of heat flow), resistances add: R_total = R1 + R2. In parallel (heat can flow through multiple paths side by side), the reciprocals add: 1/R_total = 1/R1 + 1/R2.

What are typical thermal conductivity values?

Copper: ~400 W/m·K; Aluminum: ~205 W/m·K; Steel: ~50 W/m·K; Concrete: ~1.7 W/m·K; Glass: ~1.0 W/m·K; Brick: ~0.7 W/m·K; Wood: ~0.15 W/m·K; Fiberglass insulation: ~0.04 W/m·K; Air: ~0.026 W/m·K.

How do I calculate heat flow from thermal resistance?

Heat flow Q = ΔT / R_total, where ΔT is the temperature difference across the material (in Kelvin or °C) and R_total is the total thermal resistance in K/W.

What is R-value in building insulation?

Building R-value is the thermal resistance per unit area: R_area = L / k (m²·K/W). This tool computes the full R = L/(k·A) by including actual area. To get the per-area R-value, set area to 1 m².

Thermal Resistance Calculator

Compute thermal resistance for single or multiple material layers in series or parallel configurations.

Material Layers

Configuration:

Results

Enter layer values and click Calculate.

Common Thermal Conductivities (k)

Material	k (W/m·K)

Summary

This calculator computes thermal resistance using R = L / (k × A), where L is the layer thickness, k is the thermal conductivity of the material, and A is the cross-sectional area. Add multiple layers and choose series or parallel configuration to find the total resistance of composite walls, heat sinks, or any multilayer thermal system.

How it works

Enter the thickness (L), thermal conductivity (k), and cross-sectional area (A) for each material layer.
The tool computes R = L / (k × A) for each layer.
Select Series or Parallel configuration to combine multiple layers.
For series: R_total = R1 + R2 + ... For parallel: 1/R_total = 1/R1 + 1/R2 + ...
Read the total thermal resistance and per-layer breakdown in the results panel.

Use cases

Design building walls with insulation, concrete, and drywall layers.
Analyze heat sink performance in electronics cooling.
Compare insulation materials by R-value per unit thickness.
Calculate heat flow through composite pipe walls.
Evaluate window glazing thermal performance.
Size heat exchangers for industrial processes.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu