This study presented a theoretical method to find approximated dimensions of the rectangular micro-asperity. The suitable values required for the asperity’s width and its critical length are found for different values of the flow speed. Numerical calculation is carried out using the solidworks flow simulation; the simulation results illustrated the flow speed trajectory, the variation of the shear stress and the flow pressure on different faces of the micro-asperities. The turbulence area due to the micro-asperity geometry is localized. The prediction of the maximum wear area, due to the skin friction, is also localized in consideration of the shear stress variation.