Heat conduction calculator (Fourier law)
Enter the material conductivity, wall dimensions and temperature difference to get the heat flow in watts. Useful for comparing insulation and rough cooling loads.
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How to use it
- Enter thermal conductivity k, area, temperature difference and thickness.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
P = k × A × ΔT / d, thermal resistance R = d / k, and heat transfer coefficient U = k / d.
Example
Inputs: Thermal conductivity k = 0.8 W/(m·K), Area = 10 m², Temperature difference = 20 K (°C), Thickness = 200 mm. Result: Heat flow rate: 800 W; Heat flux: 80 W/m²; Thermal resistance R: 0.25 m²·K/W.
Limits and caveats
- It covers steady conduction through one layer and leaves out surface air films and radiation.
- Conductivity varies by product and moisture, so use the manufacturer's declared value when you have it.
Questions about this tool
What are k values for common building materials?
Roughly: normal concrete 1.4 to 2, brick about 0.6 to 1, glass about 1, and mineral wool or polystyrene 0.03 to 0.04 W/(m·K).
What is the difference between R and U?
R is the layer's resistance to heat flow, higher is better insulation; U is its reciprocal, lower is better.
Kelvin or Celsius for the difference?
Either one. A difference of 1 °C equals a difference of 1 K.