Filter media is sometimes rated in U.S mesh and also in microns which makes life confusing for us all. It really comes down to where the filter media is made and which unit of measure the manufacturer chooses.
U.S mesh gauge standard is the number of openings per linear inch using standard wire diameters. Wire mesh measures the number of wires (or threads) per linear inch, not the size of the holes between them. As the number of wires per inch goes up, the size of the holes (in microns) goes down.
This chart below is a rough conversion between U.S Mesh and Microns as there is no simple formula to convert between microns and mesh because it can not account for the wire diameter.
What is the difference between 'G' Thread (7/8") and "F" Thread (11/16") airless spray guns?