Micron also called um is a length unit which is 0.001mm or 0.00003937inch, usually to describe the tiny particles size, and aperture size of the mesh fabric in industrial filtration. The Micron size of mesh should be smaller than the particle size in the fluid to capture them.
The relationship between Mesh and Micron
The higher mesh count means there are more holes and wire density in unit length, so the micron of aperture decreasing. But they are not fixed proportion as the different mesh count has different yarn diameter (thickness).