In heat transfer analysis, thermal diffusivity (usually denoted $\alpha$ but $a$, $\kappa$,$k$, and $D$ are also used) is the thermal conductivity divided by density and specific heat capacity at constant pressure. The formula is: $\alpha = {k \over {\rho c_p}}$, where k is thermal conductivity ($W/(\mu \cdot K)$), $\rho$ is density ($kg/m^{3}$), and $c_p$ is specific heat capacity ($\frac{J}{(kg \cdot K)}$) .The denominator $\rho c_p$, can be considered the volumetric heat capacity ($\frac{J}{(m^{3} \cdot K)}$).