Reading a Sieve Analysis: Mesh, Microns, and What the Percentages Really Tell You

A sieve analysis is a table that says what percentage of a bead batch sits between each pair of screen sizes. It looks like paperwork, but to someone who reads it, it is a preview of how the beads will behave on the road or in the mill. Here is the plain-English version of what those rows mean.

Mesh and microns, the two languages of size

Mesh is the count of openings per inch in a screen. Forty mesh means the screen has roughly 40 openings per linear inch, and particles that pass through are smaller than those openings. Because more openings means smaller holes, higher mesh always means finer beads. The same size is often quoted in microns: one micrometer is one thousandth of a millimeter, and 40 mesh corresponds to roughly 425 micrometers.

Suppliers switch between the two systems freely, which is where half the confusion starts. A customer asks for “20 to 40 mesh”, another asks for “850 to 425 micron”, and they are describing the same product. When in doubt, ask for the micron range, because it is unambiguous.

Common conversions at a glance

Mesh	Micron (µm)	Millimetre (mm)
16	1180	1.18
18	1000	1.00
20	850	0.85
30	600	0.60
40	425	0.425
50	300	0.30
70	212	0.212
80	180	0.18
100	150	0.15
120	125	0.125

These are the nominal openings of the standard sieve series (ASTM E11 / ISO 565). The full mesh to micron size chart covers the rest of the range, from 10 mesh down to 325 mesh, together with the grade bands we actually supply.

What the percentages tell you

A single cut like 20/40 mesh still contains a spread of sizes inside that window. The sieve report breaks it down: so many percent above 850 microns, so many between 850 and 600, and so on down to the fines below the bottom screen. Two suppliers can both call their product 20/40 mesh and ship noticeably different distributions, one heavy on the coarse end, the other with more fines. Both pass a loose description; only one is right for your job.

For drop-on road marking beads, a batch with too many fines reflects weakly, because small beads catch less light. For grinding media, an uneven distribution changes how the charge packs in the mill. That is why we include the full sieve report, not just the nominal range, and why a careful buyer reads the middle of the table, not just the top line.

Column in the report	What it means	What to watch for
Mesh or sieve number	The screen the fraction was retained on	Confirm whether the standard is US, Tyler or British; they differ
Micron opening	The nominal aperture of that screen	Should match the mesh number; a mismatch indicates a transcription error
Retained percentage	Material held on that screen	Large spikes suggest a narrow or poorly controlled cut
Cumulative passing	Total fraction finer than that screen	The most useful column for comparing two suppliers
Fines below the bottom screen	Material finer than the nominal minimum	High fines mean dust, poor flow and wasted material

Three numbers to look at first

Check the top oversize row: a compliant batch should have close to zero percent above the top screen, since oversized beads settle unevenly or clog the line. Check the middle of the distribution: the bulk of the material should sit in the intended working range rather than at the edges. And check the fines at the bottom: for most marking jobs, a few percent of fines is tolerable, but a creeping fines number usually means the screening is drifting and tomorrow’s batch may be worse than today’s.

Number	Why it matters	Red flag
Median size	Tells you what most of the batch actually is	Median far from the nominal midpoint of the range
Spread between top and bottom cut	Controls finish consistency	A very wide spread means variable results batch to batch
Fines percentage	Affects flow, dust and effective yield	More than a few percent below the bottom screen

A single report only tells you about one batch. Ask for reports across several production dates if you want to judge whether the supplier holds the grading consistently, which matters more than any individual result.

Ask for the report before the quote

Any serious supplier keeps sieve data for every batch and can share it before you commit. If a supplier hesitates or quotes only a nominal mesh, that is worth noticing. The report is free, it takes two minutes to produce, and it saves both sides from a dispute at the site gate.

Not sure which cut you need in the first place? Start from the glass bead size chart and work back to the sieve report.

Comparing two suppliers fairly

Put the cumulative passing columns for both suppliers side by side and plot them. Two gradings that look identical in the catalogue will often diverge visibly when plotted, and the divergence tells you which supplier holds a tighter distribution. That difference shows up later as finish consistency on your parts, so it is worth more attention than the quoted price difference in most cases.