Mesh size is fairly straightforward. It measures the number of openings in the mesh that make up one linear inch. For example, a 12 mesh screen means that there 12 openings across one inch. A 120 mesh screen means the openings are much smaller and that there are 120 openings per inch.

All you do is count the number of openings in one linear inch of screen. This count is the mesh number. A 4-mesh screen means there are four little square openings across one inch of screen. A 100-mesh screen has 100 openings per inch, and so on.

U.S. Mesh Size (or U.S. Sieve Size) is defined as the number of openings in one square inch of a screen. For example, a 36 mesh screen will have 36 openings while a 150 mesh screen will have 150 openings.