• Mesh as a Particle Size Measure

Mesh as a Particle Size Measure

Mesh, in particle size measurement, is a sieve-based unit that describes particle size by the number of openings per linear inch in a standardized screen, where higher mesh numbers correspond to smaller particles and lower mesh numbers to larger particles.

In mineral processing, metallurgy, and gold recovery, mesh is a practical and widely used way to classify particle sizesbased on sieving. A sieve labeled with a specific mesh number (for example, 100 mesh) has that many openings per inch; particles small enough to pass through those openings are considered smaller than that mesh size. This leads to an important practical convention: when someone says “100 mesh material”, it almost always means material that passes a 100-mesh screen, i.e. particles smaller than 100 mesh, not particles that are exactly 100 mesh in size.

To be more precise, particle sizes are often described as mesh size groups, defined by two sieves. For example, the 50–100 mesh particle size group means particles that pass through a 50-mesh sieve but are retained on a 100-mesh sieve. In practical notation, this can be expressed as <50 mesh and >100 mesh, clearly indicating the upper and lower size limits. Understanding this convention is essential, because mesh numbers decrease as particle size increases, which can initially feel counter-intuitive. A 50–100 mesh fraction is therefore smaller than 50 mesh material and larger than 100 mesh material.

Particle size groups can be expressed in several equivalent ways:

• Mesh range: 50–100 mesh
• Inequality form: <50 mesh and >100 mesh
• Micron range: approximately 300 µm down to 150 µm (depending on sieve standard)

Using micron values alongside mesh helps avoid ambiguity, especially when comparing data across laboratories, countries, or equipment standards. Below is a commonly used US mesh to micron reference table, suitable for mineral processing and gold recovery work:

US Mesh	Approx. Particle Size (micron)
3.5	5600
4	4750
5	4000
6	3350
7	2800
8	2360
10	2000
12	1700
14	1400
16	1180
18	1000
20	850
25	710
30	600
35	500
40	425
45	355
50	300
60	250
70	212
80	180
100	150
120	125
140	106
170	90
200	75
230	63
270	53
325	45
400	38
450	32
500	25
625	20

An interesting and often overlooked detail is that GNU units, a widely used scientific unit conversion tool, includes mesh particle size conversions. The mesh definitions were written by Adrian Mariano, with contributions by Jean Louis, specifically to include mesh sizes—highlighting how established and standardized mesh usage is in technical fields.

In the Start Your Own Gold Mine program, mesh measurement is used extensively for gold recovery, process control, and concentrate management. Correctly understanding mesh sizes allows operators to match crushing, milling, and classification stages to the gold liberation size, minimize gold losses, avoid over-grinding, and properly manage concentrates for further recovery or refining. In short, mesh is not just a number—it is a practical language for controlling efficiency, recovery, and profitability in small- and medium-scale gold mining operations.