Mesh vs. Microns
Sieving or screening is a method of categorizing a powder’s particle size by running the powder through a specific sized screen. Two scales are used to classify particle sizes; US Sieve Series and Tyler Mesh Size.
The mesh gauge standard measures the number of openings per linear inch using standard wire diameters. It says nothing about the size of the openings. A 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 goes down. Therefore, the larger the mesh size (the larger the number of wired) the smaller the size of the holes.
Figuring out mesh sizes is simple. All you do is count the number of openings in one inch of screen (in the United States, anyway.) The number of openings is the mesh size. So a 4 mesh screen means there are four little squares across one linear inch of screen. A 100 mesh screen has 100 openings, and so on.
Mesh size is not a precise measurement of particle size. Screens can be made with different thicknesses of wire, the thicker the wires, the smaller the particle size passing through that screen, and vice versa.
A micron is another measurement used for measuring particle size. A micron is a linear measurement of size described in metric terms. For example, we are all familiar with meters, centimeters, and millimeters. The micrometer (the U.S. spelling) is commonly known as a micron and is the size below the millimeter. It is one-millionth of a meter.
In sieving when the particle size is classified in microns, it is describing the size of openings in a given screen through which smaller particles will pass. So, as the micron size becomes smaller the size of the particles that will pass through the screen become smaller.
The chart below roughly converts between U.S. Mesh, microns, and fractions of an inch. There is no simple formula to convert between microns and wire mesh because it would have to account for changing wire diameter.