In heat transfer analysis, **thermal diffusivity** is the thermal conductivity divided by density and specific heat capacity at constant pressure.^{[1]} It measures the rate of transfer of heat of a material from the hot end to the cold end. It has the SI derived unit of m²/s. Thermal diffusivity is usually denoted *α* but *a*,h,*κ*,^{[2]} *K*,^{[3]} and *D* are also used. The formula
is:

^{[4]}

where

- is thermal conductivity (W/(m·K))
- is specific heat capacity (J/(kg·K))
- is density (kg/m³)

Together, can be considered the volumetric heat capacity (J/(m³·K)).

As seen in the heat equation,^{[5]}