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Thermal Diffusivity from Material Properties

Relate thermal diffusivity to thermal conductivity, mass density and specific heat capacity.

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

Conductivity 1 W/(m·K), density 1,000 kg/m³ and specific heat 1,000 J/(kg·K) give diffusivity 0.000001 m²/s, equal to 1 mm²/s.

Thermal diffusivity = thermal conductivity / (density × specific heat capacity)

Worked example

Enter these known values and leave the other values blank.

Illustrative material or Custom
Custom
Thermal conductivity
1 W/(m·K)
Mass density
1000 kg/m³
Mass-specific heat capacity
1000 J/(kg·K)
Thermal diffusivity
1 mm² / sec

Assumptions and limitations

  • Conductivity, density, specific heat and diffusivity are positive. Use properties measured for the same temperature, pressure, composition and material state.
  • This scalar relation describes a homogeneous isotropic material. It does not model directional conductivity, changing phase, convection or a complete temperature-versus-time solution.
  • Material presets are fixed illustrative property triples, not a live database indexed by temperature. Choose Custom for properties applicable to your conditions.
  • Calorie-based specific heats use thermochemical calories; BTU-based properties use International Table BTUs. Temperature denominators represent intervals.

Common questions

How is diffusivity different from conductivity?

Conductivity relates a temperature gradient to heat flow. Diffusivity also includes how much heat a volume stores through density and specific heat.

What happens if specific heat doubles?

With conductivity and density fixed, thermal diffusivity halves.

References

BTU-based thermal units use the International Table BTU and exact mass, time, length and temperature-interval definitions. Bookify uses exact customary mass and volume definitions for density units, replacing rounded factors in the reference. Calorie-based specific heats use the thermochemical calorie, exactly 4.184 joules, consistently with the heat-capacity units.

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