Ask what "200 mesh" means in microns and you will get several confident and slightly different answers. That is not because anyone is careless. Mesh number counts openings per linear inch, and an opening is whatever is left after the wire — so the same mesh count woven from thicker wire has a smaller aperture. This converter therefore asks for the wire diameter rather than pretending it can be guessed, and returns the aperture that geometry actually gives.
Arb Digital built the page this way deliberately. It would be easy to publish a lookup table and let readers assume it is universal, but sieve series differ, wire gauges within a series differ by grade, and a table with no stated provenance is worse than no table at all. What follows is the geometry, the standards that govern it, and the reasons the published numbers disagree.
What This Mesh to Micron Converter Does
In the forward direction, enter a mesh number and a wire diameter and the calculator returns the clear aperture in microns, millimetres, inches and mils, along with the percentage open area of the cloth. In the reverse direction, enter a target aperture and a wire diameter and it returns the mesh count that geometry implies.
The relation it implements is the woven-wire geometry that underlies the sieve series in ASTM E11 and ISO 3310-1. Both of those standards designate a sieve by its aperture — 75 µm, 150 µm, 2.00 mm — and treat the mesh number as an alternative designation carried over from older practice. Other series exist and give different microns for the same nominal mesh: the Tyler series, market-grade and mill-grade industrial cloths, and various national standards all pair mesh counts with their own wire gauges. If your specification names a series, use the wire diameter from that series rather than the value another one would give.
This page converts a woven-cloth geometry. It is not a particle-size analysis, and passing a sieve does not mean a particle is smaller than the aperture in every dimension — an elongated particle can pass end-on. If you need general unit conversion rather than sieve geometry, the length converter and the broader unit converter handle that directly.
How to Use It
- Choose the direction. Mesh to aperture is the usual case; the reverse tells you what mesh count a target opening implies for a given wire.
- Enter the mesh number as openings per linear inch. This is always the linear count, never per square inch.
- Enter the wire diameter and its unit. Take it from the cloth specification, the sieve certificate or the supplier's data sheet. This is the input that makes the answer specific rather than approximate.
- Read the aperture in the hero figure and its equivalents in the grid, with the open area of the cloth alongside.
- Check the pitch shown under the headline figure — it is the wire-to-wire spacing, and the aperture can never exceed it.
The Formula: How It's Calculated
A square-weave cloth repeats on a pitch of one inch divided by the mesh count. One inch is exactly 25,400 microns, so:
pitch (µm) = 25,400 ÷ mesh, and aperture = pitch − wire diameter
Reversed, mesh = 25,400 ÷ (aperture + wire diameter). The percentage open area of a square weave is the ratio of open area to total area in one repeating cell, which is (aperture ÷ pitch)² × 100.
A worked example, matching the defaults on this page: at 200 mesh the pitch is 25,400 ÷ 200 = 127 µm. With a wire diameter of 53 µm the aperture is 127 − 53 = 74 µm, which sits alongside the 75 µm aperture that ASTM E11 designates for its No. 200 sieve. The open area is (74 ÷ 127)² = 33.95%, so about a third of the cloth is hole and two-thirds is wire. That last figure is worth internalising: fine sieve cloth is mostly metal, which is why fine screening is slow.
The sieve series themselves, the tolerances on aperture and wire diameter, and the relationship between the ASTM and ISO designations are described in Gilson's guide to U.S. and metric sieve sizes, and the technical requirements for the cloth are specified in ASTM E11, Standard Specification for Woven Wire Test Sieve Cloth and Test Sieves. The equivalent international standard is ISO 3310-1, Test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth.
Why Two Sources Give Different Microns for the Same Mesh
Because the mesh number fixes only the pitch. The aperture is the pitch minus the wire, and the wire is a free variable chosen by whoever specified the cloth. A 100 mesh cloth has a 254 µm pitch by definition. Woven with 100 µm wire it opens to 154 µm; woven with 66 µm wire it opens to 188 µm. Both are honestly "100 mesh", and they differ by 22%.
That is the whole explanation for the disagreements between published tables. Test-sieve series such as ASTM E11 and ISO 3310-1 fix a nominal wire diameter for each aperture, so within those series the mesh-to-micron mapping is well defined. The Tyler series was built around a different progression and pairs some mesh counts with different apertures. Industrial filter cloths sold as market grade, mill grade or tensile-bolting cloth deliberately vary the wire gauge at a fixed mesh to trade open area against strength, and their apertures are correspondingly different.
The practical rule is simple: quote a specification by aperture, not by mesh. If a document says "100 mesh" and nothing else, it has not specified an opening size, and the sensible response is to ask which series and which wire gauge.
Open Area: The Number That Predicts Throughput
Open area is the fraction of the cloth that is actually hole, and it governs how fast material or fluid gets through far more directly than aperture alone. It falls quickly as cloth gets finer, because the wire cannot be thinned in proportion without becoming too weak to weave and handle. A 20 mesh cloth with 0.4 mm wire has a pitch of 1,270 µm and an aperture of 870 µm — 46.9% open. A 325 mesh cloth with 36 µm wire has a pitch of 78.2 µm and an aperture of 42.2 µm — only 29.1% open.
Two cloths can therefore share an aperture and behave very differently. Choosing a heavier wire at the same mesh buys abrasion resistance and life at the direct cost of open area, and therefore of capacity. For screening, that shows up as reduced throughput; for filtration, as a higher pressure drop for the same flow, which is where the pipe flow calculator and the porosity and permeability calculator pick up the story.
What a Sieve Result Does and Does Not Tell You
A particle passes a square aperture if its two smallest dimensions fit. Its longest dimension is irrelevant, so a needle-shaped particle many times longer than the aperture will pass end-on given enough agitation. Sieve analysis therefore measures a particle's second-smallest dimension, not its length, volume or equivalent sphere diameter. Laser diffraction and image analysis measure different things again, which is why the same powder can produce three different "particle size distributions" from three different instruments without any of them being wrong.
Sieving is also a kinetic process rather than an instantaneous test. A near-mesh particle needs many presentations to the cloth at the right orientation before it passes, so results depend on sieving time, amplitude and loading. Overloading a sieve is the most common error in practice: too deep a bed means particles never reach the cloth, and the result reports a coarser distribution than the material really has. Standard methods set both a time and a maximum loading for exactly this reason.
Blinding — particles wedging in and plugging apertures — progressively reduces open area during a test and biases the result the same way. It is worst when the feed contains a lot of near-aperture material or anything sticky, and it is the reason sieve stacks are inspected and cleaned between runs rather than simply reused.
Wear, Tolerance and Why Sieves Are Recertified
Sieve cloth is a precision product with published tolerances, and it does not stay in specification indefinitely. Standards allow a tolerance band on the average aperture, a wider band on any individual aperture, and a tolerance on wire diameter. A cloth can be fully compliant and still sit at one end of that band, which is another reason two nominally identical sieves do not give identical results.
In service the wires abrade, stretch and occasionally break. Abrasion thins the wire, which increases the aperture — a worn sieve passes coarser material than a new one, so its results drift steadily in one direction rather than becoming noisy. That is why laboratories recertify sieves on a schedule and inspect them for damage between uses, and why comparing a result from a well-used sieve against one from a new sieve is not a like-for-like comparison. Weighing the retained fractions accurately matters just as much; the percentage calculator handles the mass-fraction arithmetic if you are working a distribution by hand.
Arb Digital builds precise, fast calculators that answer the questions your customers actually search for, and keeps them accurate. Browse what we have published, or tell us what your audience needs.
Browse All Free Tools Talk To Arb DigitalCommon Mistakes to Avoid
- Treating mesh number as an opening size — it fixes the pitch only, and the aperture depends on the wire diameter woven into that pitch.
- Mixing series — an ASTM E11 wire gauge and a Tyler or mill-grade one give different apertures at the same mesh count, so pick one and stay in it.
- Reading mesh as openings per square inch — it is always the count along one linear inch.
- Assuming everything that passes is smaller than the aperture — elongated particles pass end-on, so a sieve sizes on the second-smallest dimension.
- Overloading the sieve — a deep bed prevents particles reaching the cloth and reports the material as coarser than it is.
Related Free Tools From Arb Digital
For plain unit conversion between microns, millimetres and inches, use the length converter or the general unit converter. Mass fractions from a sieve stack are quick work in the percentage calculator and the ratio calculator. For what happens to fluid passing through a porous medium, see the porosity and permeability calculator, the pipe flow calculator and the Reynolds number calculator. Material densities for converting a retained mass to a volume come from the density calculator. Everything else is in the free online tools hub.
Frequently Asked Questions
It depends on the wire diameter. At 200 mesh the pitch is 127 microns, so with 53 micron wire the aperture is 74 microns. ASTM E11 designates its No. 200 test sieve as 75 microns. A cloth of the same mesh count woven with heavier wire would have a noticeably smaller opening.
Because they assume different wire diameters. Mesh number only fixes the wire-to-wire pitch; the clear opening is that pitch minus the wire. Test-sieve series such as ASTM E11 and ISO 3310-1 pair each mesh count with a nominal wire, but Tyler, market-grade and mill-grade cloths use different gauges and therefore give different apertures.
Per linear inch. A 100 mesh cloth has 100 openings and 100 wires across every inch measured in a straight line, which works out to 10,000 openings in a square inch for a square weave, but the mesh number itself is always the linear count.
For a given wire gauge, yes, because the pitch shrinks. Across different cloths it is not guaranteed, since a coarser mesh woven with very fine wire can have a larger open area and a comparable aperture to a finer mesh woven with heavy wire. Compare apertures, not mesh numbers.
It is the percentage of the cloth that is actually hole rather than wire, calculated as the square of the aperture divided by the pitch. It predicts throughput and pressure drop far better than aperture alone, and it falls sharply in fine cloths because the wire cannot be thinned in proportion.
Coarser. Abrasion thins the wires, and a thinner wire in the same pitch leaves a larger opening. The drift is systematic in one direction rather than random, which is why test sieves are inspected and recertified on a schedule rather than used until they visibly fail.
Yes, if it is elongated. A particle passes when its two smallest dimensions fit through the opening, so a needle-shaped grain many times longer than the aperture can pass end-on. Sieving therefore characterises the second-smallest dimension, which is one reason it disagrees with laser diffraction results.
This tool is provided for educational and engineering-estimate use. It applies the nominal square-weave geometry and does not account for aperture and wire tolerances, weave type, cloth wear or the sieving conditions that affect a real separation. Where a specification, a test method or a product claim depends on the result, use the aperture stated on the sieve certificate and the applicable standard.
