# Thermal diffusivity

In heat transfer analysis, thermal diffusivity (symbol: $\alpha$) is the ratio of thermal conductivity to volumetric heat capacity.

$\alpha = {k \over {\rho c_p}}$

where:

The SI units for thermal diffusivity are square metres per second or m2âˆ™s-1.

Substances with high thermal diffusivity rapidly adjust their temperature to that of their surroundings, because they conduct heat quickly in comparison to their thermal 'bulk'. For common rock material, $\alpha \approx$ 10-2 cm2âˆ™s-1.