The Sherwood number ($Sh$) is a dimensionless parameter used in fluid mechanics and heat transfer to characterize the mass transfer rate in a fluid flow system. It represents the ratio of convective mass transfer to molecular diffusion, analogous to the Nusselt number for heat transfer. The Sherwood number can be expressed mathematically as,

​

Where:

• $Sh$ is the Sherwood number,
• $h$ is the convective mass transfer coefficient, 
• $L$ is a characteristic length scale of the flow,
• $D$ is the mass diffusivity of the fluid.