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Thermal Conductivity Calculator

Work out thermal conductivity instantly with clear inputs, formula shown and shareable results.

About Thermal Conductivity Calculator

Fourier's law gives steady conduction as Q = kA.dT/d. A 15 m2 wall of 100 mm insulation at k = 0.04 loses 120 W across a 20 K difference, or 2.9 kWh a day. Thickness sits on the bottom, so doubling insulation halves the loss - with diminishing returns as other paths dominate.

Formulas

Fourier's law

Q = k A dT / d

Layer resistance

R = d / k

Worked example

With the default values below, Thermal Conductivity Calculator returns Rate Of Heat Flow of 120.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Thermal conductivity kminimum 0 W/(m K)
0.04 W/(m K)
Area of heat flowminimum 0 m2
15 m2
Temperature difference across it
20 K
Material thicknessminimum 0 m
0.1 m

Results

Rate Of Heat Flow
120.00 W
Heat Flux Density
8.000 W/m2
R-Value Of The Layer
2.5000 m2 K/W
Energy Lost Per Day
2.880 kWh

Step by step

  1. 1Values used
  2. 2Fourier's law
  3. 3Layer resistance
  4. 4Rate Of Heat Flow= 120.00 W
  5. 5Heat Flux Density= 8.000 W/m2
  6. 6R-Value Of The Layer= 2.5000 m2 K/W
  7. 7Energy Lost Per Day= 2.880 kWh

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What are typical conductivities?

About 0.03-0.04 for mineral wool and foam, 0.6 for water, 1.0 for brick, 45 for steel and 400 for copper.

Why quote R-value rather than k?

Because R combines conductivity with thickness and adds up across a construction, so a wall's total resistance is the sum of its layers.

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