Mesh counts particles per inch of screen; micron measures particle diameter. They are not two names for the same thing, and the conversion between them is a range rather than a number. If you compare suppliers using only the grade label, you can end up with powder that is one full step coarser or finer than you intended.
Two Different Measuring Systems
Mesh is a screening concept. A 325 mesh screen has 325 openings per linear inch, so the number describes the screen, not the particle. Micron describes the particle itself, usually as the nominal upper limit of a size band.
That difference explains most of the confusion in purchase orders. A buyer who asks for “325 mesh” is asking for what passed through a screen. A buyer who asks for “W40” is asking for a particle band whose upper limit is 40 micrometres. The two requests can overlap without being equal.
Mesh In Practice
Mesh dominates the coarse end of the market because screening is how those sizes are actually produced and checked. Saw blade grit, drill grit, electroplated tool grit and milled crushed material are all bought and sold in mesh.
Mesh grades are written as a pair, such as 40/45 or 80/100. The two numbers are the screens the material passed and was retained on. A 40/45 grit passed a 40 mesh screen and stayed on a 45 mesh screen, so the particles sit between those two openings.
Mesh is also where single-particle strength matters most. A saw blade segment holds each particle in a metal matrix and depends on it to cut stone without fracturing in the first few minutes. That is why the mesh end of the catalogue is dominated by high-strength material such as MBD grit, not by milled micron powder.
Micron And W-Series In Practice
The W-series is the standard fine-grades language. The number after W is the nominal upper limit in micrometres, and each grade covers a defined band below it. W40 runs from about 40 down to 28 micrometres; W10 runs from about 10 down to 7; W1 runs from about 1 down to 0.5.
Below W1, the trade switches to nanometre descriptions entirely. HDYM covers W0.5 to W0.1 and HDPN covers 5 to 500 nanometres, because micrometre labels stop being useful once the particle is smaller than the wavelength of visible light.
Conversion Table
The table below maps the mesh grades used in this catalogue to their nominal micron window. Treat it as a bridge for reading documents, not as a purchase specification.
| Mesh grade | Nominal micron window | Nearest W grade |
|---|---|---|
| 30/35 | 500 – 600 | Coarser than W50 |
| 40/45 | 355 – 425 | Coarser than W50 |
| 50/60 | 250 – 300 | Coarser than W50 |
| 60/70 | 212 – 250 | Coarser than W50 |
| 80/100 | 150 – 180 | Coarser than W50 |
| 100/120 | 125 – 150 | Coarser than W50 |
| 140/170 | 90 – 106 | Coarser than W50 |
| 170/200 | 75 – 90 | Coarser than W50 |
| 200/230 | 63 – 75 | Coarser than W50 |
| 230/270 | 53 – 63 | W50 |
| 270/325 | 45 – 53 | W50 / W40 |
| 325/400 | 38 – 45 | W40 |
| 400/500 | 25 – 38 | W28 / W40 |
| 500/600 | 20 – 25 | W20 / W28 |
Why The Conversion Is Not Exact
Three things break the neat one-to-one mapping:
- Screen openings are not round. An elongated particle can pass a screen that a round particle of the same width cannot. Mesh controls one dimension; laser diffraction measures an equivalent sphere.
- Different standards. US mesh, FEPA F and P designations, and JIS all use different wire diameters and opening tolerances at the same number. “400 mesh” is not a universal quantity.
- Measurement method. Sieve results and laser-diffraction results on the same powder will not agree exactly, because they measure different physical properties.
Common Mistakes
- Converting with a single number. Charts that say “W40 equals 400 mesh” are approximations that hide the whole problem. Use the range, then confirm with the certificate.
- Assuming a coarser mesh is always tougher. Strength comes from the crystal grade, not from the screen size. A high-strength fine grit can outperform a weak coarse one in the same bond.
- Ignoring which end of the band your process needs. Two powders both labelled W20 can differ by several micrometres at D90, which is exactly the range that produces visible scratches.
How To Verify
Ask for three things and the mesh-versus-micron question usually answers itself: the mesh range or W grade in writing, the laser-diffraction PSD for that lot, and the screening standard used. If a supplier can only give you the grade name, they are telling you they do not measure the product.
For coarse material, a sieve analysis plus a morphology image is enough. For W-series and finer, insist on laser diffraction, because screening stops being reliable below roughly 40 micrometres.
Next Step
Coarse mesh grit for bonded tools: MBD high-strength grit from 18/20 to 500/600 mesh. Black raw grit in the mid range: HDGD 50/60 to 140/170. Fine powder: HDY W50 to W1.
Then match the size to the tool: saw blades and core drills for mesh grades, electroplated tools for the 80 to 400 mesh band.