Using the heat-mass transfer analogy, a mass transfer St equivalent can be found using the Sherwood number and Schmidt number in place of the Nusselt number and Prandtl number, respectively.
where
*  is the mass Stanton number;
* is the Sherwood number based on length;
* is the Reynolds number based on length;
*  is the Schmidt number;
*  is defined based on a concentration difference (kg s m);
*  is the velocity of the fluid