Understanding Mesh Sizes and Microns

What does mesh size mean? 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. Note, therefore that as the number describing the mesh size increases, the particle size decreases. Higher numbers = finer powder. 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.

What do the minus ( - ) and plus ( + ) plus signs mean when describing mesh sizes? Here’s a simple example of how they work. -200 mesh aluminum would mean that all particles would pass through a 200 mesh screen. A +200 mesh aluminum means that all the particles are retained on a 200 mesh screen.

How fine do screens get? That depends on the wire thickness. If you think about it, the finer the weave, the closer the wires get together, eventually leaving no space between them at all. So, beyond 325-400 mesh, we usually describe particle size in "microns."

What is a micron? A micron is another measurement we use for measuring particle size. A micron is one-millionth of a meter or one twenty-five thousandth of an inch.

This table is adapted from a post made by Ken Kosanke to the PML and previously published in a PGII Bulletin.

U.S. Standard *	Space between wires
Sieve Mesh No.	Inches	Microns**	Typical material
14	0.056	1400
28	0.028	700	Beach sand
60	0.0098	250	Fine sand
100	0.0059	150
200	0.0030	74	Portland cement
325	0.0017	Silt	44
400	0.0015	37	Plant Pollen
(1200)	0.0005	12	Red Blood Cell
(2400)	0.0002	6
(4800)	0.0001	2	Cigarette smoke

* The mesh numbers in parentheses are too small to exist as actual screen sizes; they are estimated and included just for reference.