To determine the mesh size of a sieve, count the number of openings in 1 linear inch of screen. Mesh sizes also indicate the size of the holes in the screen.
To find the mesh size, place a ruler along any length of wire on the screen. Counting the openings gives the mesh size. This number also corresponds to the opening size. There are two classification scales used for sieves: the US Sieve Series and the Tyler Mesh Size or Tyler Standard Sieve Series.
The Tyler Mesh Size range begins with the largest screen opening. A size 2 1/2 mesh has a width of 8 millimeters, while a size 3 mesh has openings of 6.73 millimeters. As the openings become smaller, the two scales remain similar, but the mesh size numbers do not match exactly. However, the opening sizes are the same, decreasing by approximately 1/100 of a millimeter per level on the scales. Both scales range in mesh sizes of 3 1/2 to 400, with 3 1/2 corresponding to an opening size of 5.66 millimeters and 400 to 0.037 millimeters. Higher mesh size therefore indicates a larger number of openings of smaller size. Opening size also gives an indication of the particle sizes that can pass through the screen. Wire diameter also affects opening size. Due to imperfections and irregularities, such as bent wires, not all openings are exactly the same size.