The standard sieve series in both numbering systems, plus the geometry the numbers came from — because a mesh count on its own has never specified a hole.
Calculator
Common:
200 mesh, ASTM E11 (US Standard)
75 µm
2.95 mil · 0.075 mm · the same designation in both series
What a mesh number physically is
Wire-to-wire pitch254.0 µm25 400 ÷ 100, exactly
Actual opening139.7 µmpitch minus the wire
Open area30.2%the square of the opening ratio
Same count, wire 22% thinner164.8 µm25.1 µm larger, and 11.9 points more open
There is no conversion from mesh to microns. A mesh number counts wires per inch, so the hole is the spacing minus the wire, and the two rows above are the same 100-mesh cloth woven differently. That is why standards bodies moved to designating a sieve by its aperture and kept the mesh number only as a name: the number alone never specified the screen.
The standard sieve series
Ordered by aperture — note the mesh numbers running the other way
Aperture
US (ASTM E11)
Tyler
In mil
20 µm
635
—
0.79
25 µm
500
—
0.98
32 µm
450
—
1.26
38 µm
400
400
1.50
45 µm
325
325
1.77
53 µm
270
270
2.09
63 µm
230
250
2.48
75 µm
200
200
2.95
90 µm
170
170
3.54
106 µm
140
150
4.17
125 µm
120
115
4.92
150 µm
100
100
5.91
180 µm
80
80
7.09
212 µm
70
65
8.35
250 µm
60
60
9.84
300 µm
50
48
11.81
355 µm
45
42
13.98
425 µm
40
35
16.73
500 µm
35
32
19.69
600 µm
30
28
23.62
710 µm
25
24
27.95
850 µm
20
20
33.46
1000 µm
18
16
39.37
1180 µm
16
14
46.46
1400 µm
14
12
55.12
1700 µm
12
10
66.93
2000 µm
10
9
78.74
2360 µm
8
8
92.91
3350 µm
6
6
131.89
4750 µm
4
4
187.01
Read the two middle columns together going down. They mostly agree at the ends and come apart in the middle — US 140 and Tyler 150 are the same 106 µm sieve, and so are US 70 and Tyler 65. The Tyler series was numbered from a 200-mesh cloth originally specified at 74µm; the apertures were later harmonised but the numbering was not. A specification that says only “150 mesh” therefore names two different screens depending on who wrote it.
Nearest sieve to 100 µm
Standard aperture106 µm6.0% from what you asked for
DesignationsUS 140Tyler 150
Sieve apertures come from a fixed geometric series rather than a continuous scale, so an arbitrary micron figure lands between two of them. Specifying a sieve that is not in the series means having cloth woven to order, which is why particle specifications are usually written to the nearest standard sieve rather than to a round number.
What the plus and minus mean
−200 meshpassedPassed a 75 µm sieve. Somewhere below 75 µm, with no lower bound stated.
+200 meshretainedRetained on a 75 µm sieve. Somewhere above 75 µm, with no upper bound stated.
Neither is a particle size. Both are statements about a boundary in a distribution: one says the material got through a hole, the other says it did not. A powder described as −200 mesh may be almost all just under the aperture, or almost all far below it, and the description cannot tell them apart. That is what a full sieve analysis, reporting the percentage retained on each of several screens, exists to say.
When a sieve stops measuring size
How particle shape changes what a sieve reports
Shape
What the sieve actually measures
Near-spherical — sand, shot, most catalysts
Sieve aperture and particle diameter agree closely. This is the case the tables assume.
Needles and fibres — wollastonite, milled glass fibre
Passes end-on through a sieve far smaller than its length. A 200-mesh fibre may be a millimetre long.
Plates and flakes — mica, graphite, some clays
Passes edge-on. Sieve size reports thickness far more than it reports diameter.
Agglomerates — pigments, spray-dried powders
Sieves as clusters unless dispersed, so the result depends on how hard the sample was worked.
A sieve sorts on the second-largest dimension, because that is what has to fit through a square hole. For sand that is the same as a diameter. For a fibre it is the thickness, and a “200 mesh” milled glass fibre can be a millimetre long. This is the usual reason a sieve analysis and a laser diffraction result disagree — they are not measuring the same property, and neither is wrong.
The current aperture in every length unit
Unit
Value
Note
micrometre (µm)
75.000
Also written micron. The unit particle sizes are quoted in.
thousandth of an inch (mil)
2.953
Exactly 25.4 µm. Not a millimetre, despite the name — the commonest confusion on a spec sheet.
millimetre (mm)
0.075
Coarse sieves are designated in these rather than in mesh.
inch (in)
0.00295
Exactly 25 400 µm, and the length a mesh number counts wires across.
What this converter covers
Thirty standard apertures with US and Tyler designations, the woven-cloth geometry, and what a plus or minus in front of a mesh number does and does not assert.
US (ASTM E11) and Tyler mesh numbers against nominal apertures
The real opening from a mesh count and a wire diameter, plus open area
Microns, mils, millimetres and inches
What −200 and +200 mesh mean, and what they leave unsaid
Where particle shape breaks the assumption that a sieve measures size
Two numbering systems Wire diameter required Shape caveats µm · mil · mm · in
Free, no signup — exact by definition, not an estimate.
Updated 8 September 2026
At a glance
Formula shown
pitch = 25 400 ÷ mesh · opening = pitch − wire diameter · open area = (opening ÷ pitch)²
Scenario support
200 mesh is 75 µm · 100 mesh is 140 µm with 4.5 mil wire and 165 µm with 3.5 mil
Educational estimate
Planning support from the values you enter — not professional advice.
Mesh is not a size
A mesh number does not describe a hole. It counts wires — how many cross one inch of cloth — and the hole is whatever is left between them.
Which means the opening depends on the wire as much as on the count:
One hundred wires per inch, woven three ways
Wire diameter
Opening
Open area
4.5 mil
139.7 µm
30.2%
4.0 mil
152.4 µm
36.0%
3.5 mil
165.1 µm
42.3%
Three screens, all correctly described as 100 mesh, with openings 25 µm apart and open areas differing by twelve points. The pitch is identical in every row — 25,400 µm divided by 100 — and it is the only part of the arithmetic that the mesh number determines.
This is why the standards bodies moved. ASTM E11 and ISO 3310-1 designate a test sieve by its aperture, and keep the mesh number only as a legacy alternative name. The lookup panel above gives the standard’s aperture; the geometry panel gives the physical answer; and the two exist separately because they are answering different questions.
For a test sieve, the standard designation settles it. For industrial screen cloth, filter mesh or a bag filter rated in mesh, it does not — there, the wire diameter is part of the specification and a mesh number alone is incomplete.
Two numbering systems
A second problem sits on top of the first: there are two mesh numbering runs in common use, and they do not line up.
The Tyler series was numbered from a 200-mesh cloth originally specified at 74 µm, woven with 0.0021 inch wire, and everything else was numbered by halving and doubling from there. The US series was built around the standard aperture progression instead.
Where the two numbering runs come apart
Aperture
US (ASTM E11)
Tyler
425 µm
40
35
212 µm
70
65
125 µm
120
115
106 µm
140
150
75 µm
200
200
They agree at 200 and at the coarse end, and drift apart in between — and the 106 µm row is the awkward one, because the Tyler number is larger than the US number there while it is smaller everywhere above.
So “150 mesh” names a 106 µm sieve if the specification is Tyler and a screen between 100 and 106 µm if it is US. On a supplier’s datasheet the difference is a few per cent; on a material specification that a batch either passes or fails, it is a different test.
The scale runs backwards
This one is simple and it still catches people, including people who use it daily.
A bigger mesh number is a smaller particle. 400 mesh is finer than 100 mesh, because more wires per inch means smaller gaps between them. It is the same inversion as wire gauge, drill gauge and sheet metal gauge, and it has the same cause: the number counts something that goes up as the thing you care about goes down.
The table in the calculator is deliberately sorted by aperture rather than by mesh number, so the inversion is visible running down the page instead of being asserted in a sentence. The mesh columns descend while the microns ascend, and seeing that once is worth more than remembering a rule.
The practical consequence is in ordering and in filtration. Going “up a mesh” means going finer, so a filter change from 100 to 200 mesh halves the particle that gets through and roughly halves the flow at the same time. Getting the direction wrong produces either a blocked line or an unfiltered one, and both are discovered downstream.
Plus, minus, and what they do not say
Powders are constantly specified as “−200 mesh” or “+325 mesh”, and the notation is precise about one thing and silent about everything else.
A minus means the material passed that sieve. A plus means it was retained on it. Neither is a particle size: each is one edge of a distribution with nothing said about the other edge.
A powder described as −200 mesh might be tightly grouped just under 75 µm, or it might be mostly 10 µm dust, and the two behave completely differently in everything from flow to reactivity to how much of it becomes airborne when the bag is opened. The description cannot distinguish them.
A range does better — “−100 +200 mesh” bounds the material on both sides — and a full sieve analysis, reporting the percentage retained on each of several stacked screens, does better still. That is the form a specification takes when the distribution actually matters, and it is why a single mesh figure on a datasheet is a starting point rather than an answer.
What a sieve actually measures
There is one more assumption buried in every mesh-to-micron conversion, and it is about the particle rather than the screen.
A sieve sorts on the second-largest dimension. A particle passes if its two smaller dimensions fit through a square hole; the longest one is irrelevant, because the particle can go through end-on.
For sand, shot or a spherical catalyst that is effectively a diameter, and the conversion means what everyone assumes it means. For a fibre it is the thickness: milled glass fibre described as 200 mesh may be a millimetre long and pass a 75 µm screen without difficulty. For mica or graphite flakes it reports the thickness and says nothing about the plate diameter, which is usually the property that matters.
This is the everyday reason a sieve analysis and a laser diffraction result disagree on the same material, sometimes by a factor of several. Laser diffraction reports an equivalent spherical diameter from how the particle scatters light; sieving reports whether it fits through a hole. Neither is wrong, they are not the same measurement, and a specification written against one cannot be verified with the other.
Which is worth knowing before converting anything: the number this page produces describes a screen accurately, and describes a particle only as well as that particle resembles a sphere.
Related calculators
Other gauge, size and materials tools:
Wire GaugeAWG and SWG to mm, mm² and circular mils, with resistance and voltage drop — and the 14–21% gap the equivalence charts hide.
Sheet Metal GaugeGauge to thickness for steel, galvanised, stainless and aluminium — four standards sharing one set of numbers, up to 38% apart.
LengthMillimetres to miles on the exact 1959 factors, with the mil kept clearly apart from the millimetre — they differ 25-fold.
Textile WeightYarn counts between tex, denier, Nm and Ne, and fabric weight between GSM and ounces — keeping them apart, because no factor connects them.
Densitykg/m³, lb/ft³, lb/in³ and lb/gal, with specific gravity against any water reference and the API scale that runs backwards.
PPMppm to percent, mg/L and µg/m³ — asking which liquid or which gas, because without that the conversion has no answer.
The sieve series and the two sets of designations come from the specification that defines them; the exact inch is what makes the wire pitch exact; and the reference materials note is here because it is the reason particle sizing is technique-specific rather than absolute.
ASTM E11 — Standard Specification for Woven Wire Test Sieve Cloth and Test SievesASTM International · verified 2026-09-08 · The nominal apertures of the standard sieve series, the US alternative sieve designations shown against them, and the Tyler equivalent designations — including the places in the middle of the range where the two numbering runs diverge
Standard Reference MaterialsNational Institute of Standards and Technology · verified 2026-09-08 · That particle-size measurement is traceable through certified reference materials specific to the technique used, which is the practical form of the point that a sieve result and a laser diffraction result are measuring different properties of the same powder
SI units — lengthNational Institute of Standards and Technology · verified 2026-09-08 · That the inch is exactly 25.4 millimetres by international agreement, which makes the wire pitch of 25 400 µm divided by the mesh count an exact quantity even though the opening it implies is not
Conversion note
The apertures listed are the nominal designations of the standard series. A real sieve is manufactured to a tolerance on both the average aperture and the maximum individual opening, and those tolerances widen in relative terms as the cloth gets finer — so two conforming 400-mesh sieves do not behave identically. Sieves also wear: apertures open with use and a screen that has passed thousands of samples is no longer the sieve it was certified as, which is why laboratories recalibrate or replace them on a schedule. The geometry panel assumes plain square weave; twilled, Dutch and other weaves have different open areas and different effective openings for the same wire and count. Results from sieving are not interchangeable with results from laser diffraction, image analysis or sedimentation, which measure different properties and will disagree, sometimes substantially, on the same material. For any specification that has to be met — pharmaceutical, aggregate, or contractual — use the sieve designation and test method named in that specification rather than converting between systems.
Published the Mesh to Micron Converter: thirty standard sieve apertures from 20 to 4750 micrometres with their US (ASTM E11) and Tyler designations, in microns, mils, millimetres and inches.
States the thing a conversion table cannot: a mesh number counts WIRES PER INCH, so the opening is the wire spacing minus the wire diameter, and the same 100-mesh cloth is 140 micrometres with 4.5 mil wire and 165 with 3.5 mil.
Provides the geometry separately from the lookup and requires a wire diameter for it, refusing when the wire is thicker than the pitch -- which is a sheet rather than a screen.
Shows where the two numbering systems diverge. US 140 and Tyler 150 are the same 106 micrometre sieve, and US 70 pairs with Tyler 65, so a bare '150 mesh' specification names two different screens depending on who wrote it.
Orders the table by APERTURE rather than by mesh number, so the inversion -- a bigger number is a smaller particle -- is visible running down the page instead of being asserted in prose.
Explains that minus and plus in front of a mesh number describe a boundary in a distribution rather than a size: a minus 200 mesh powder may be tightly grouped just under 75 micrometres or mostly 10 micrometre dust, and the description cannot tell them apart.
Records that a sieve sorts on the SECOND-LARGEST dimension, so a milled glass fibre described as 200 mesh may be a millimetre long, and mica flakes report their thickness rather than their diameter -- the usual reason sieving and laser diffraction disagree on the same material.
Verified by 141 automated cases, asserting that the same mesh count with two wire diameters gives openings more than 20 micrometres apart, that US 140 and Tyler 150 resolve to one aperture while their numbers differ, that aperture ascends while mesh number descends on every adjacent pair in the table, and that a wire as thick as the pitch is refused.
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