Call our counter and ask for "50 mesh" and the first thing we'll ask back is: what wire diameter? That surprises people. Mesh count alone doesn't tell you how big the holes are, and the holes are usually what you actually care about. This article walks through the three ways woven wire mesh gets specified: mesh count, opening size, and microns. Once you see how they fit together, reading a mesh spec (or writing one) gets a lot easier.
What Does Mesh Count Mean?
Mesh count is the number of openings per lineal inch, counted from the center of one wire to the center of the wire one inch away. A 10 mesh screen has 10 openings per inch in each direction. A 100 mesh screen has 100. When both directions have the same count, we call it a square mesh, and most stock material is exactly that.
Higher mesh count means a finer screen. That part is intuitive. What trips people up is assuming the count tells you the opening size. It doesn't, because part of every inch is taken up by the wires themselves.
One more wrinkle worth knowing: very coarse mesh (roughly 1/2" openings and up) is usually specified by opening size directly, sometimes called space cloth. Mesh count takes over as the common language somewhere around 3 or 4 mesh and finer.
Why Wire Diameter Changes Everything
Picture one inch of 10 mesh screen. That inch contains 10 openings and 10 wires. If the wires are thick, they eat up more of the inch and the openings shrink. If the wires are thin, the openings grow. Same mesh count, different hole size.
The math is simple:
Opening = (1 ÷ mesh count) − wire diameter
Take 100 mesh woven with .0045" diameter wire, which is the common commercial spec:
- 1 ÷ 100 = .010" of space for each opening plus one wire
- .010" − .0045" wire = .0055" opening
Now weave that same 100 mesh with heavier .0055" wire and the opening drops to .0045". Same count, a noticeably smaller hole, and a stiffer, more durable cloth. That's why a real mesh spec always includes both numbers: count and wire diameter, written something like "100 x 100 mesh, .0045" wire." If a drawing or an order only gives you one of the two, the spec isn't complete. Our opening and open-area calculator does this arithmetic for any count and wire combination.
Microns: The Language of Filtration
Once openings get small, inches turn clumsy. Nobody wants to talk about a .0017" hole. So fine mesh, especially anything used for filtering or sieving, gets specified in microns. A micron is one millionth of a meter, or 0.001 mm. There are 25,400 microns in an inch, so converting is straightforward: multiply the opening in inches by 25,400.
Our 100 mesh example: .0055" x 25,400 = about 140 microns. For a rough feel, a human hair runs somewhere around 50 to 100 microns depending on whose head it came from, so a 100 mesh screen will stop most hairs, beach sand, and coffee grounds, but not fine silt or flour dust.
Because micron ratings depend on both count and wire diameter, a conversion is only valid for a specific weave spec. That's why our mesh-to-micron chart lists the standard commercial wire diameter alongside each count. If someone hands you a bare "mesh to micron" number with no wire diameter attached, treat it as approximate.
Open Area: How Much of the Screen Is Actually Hole
The fourth number on a good mesh spec is open area, the percentage of the screen's surface that is opening rather than wire. It drives how freely air, water, or product moves through the mesh, and how quickly a screen blinds over with debris.
The formula: open area % = (opening x mesh count)² x 100.
For 100 mesh, .0045" wire: (.0055 x 100)² = .55² = about 30% open area. Nearly seventy percent of that screen is wire. Two screens can have identical openings and very different open areas, which matters a lot when flow rate or pressure drop is part of the job. If you're sizing mesh for a strainer or a screen deck, our filtration and sieving guide goes deeper on choosing for flow versus particle retention.
Common Mesh Sizes at a Glance
These are standard commercial (market grade) specs in the diameters we stock most often. The openings and open areas follow directly from the formulas above.
| Mesh Count | Wire Diameter | Opening | Microns (approx.) | Open Area |
|---|---|---|---|---|
| 4 mesh | .047" | .203" | 5,156 | 66% |
| 10 mesh | .025" | .075" | 1,905 | 56% |
| 20 mesh | .016" | .034" | 864 | 46% |
| 40 mesh | .010" | .015" | 381 | 36% |
| 80 mesh | .0055" | .007" | 178 | 31% |
| 100 mesh | .0045" | .0055" | 140 | 30% |
| 200 mesh | .0021" | .0029" | 74 | 34% |
| 325 mesh | .0014" | .0017" | 43 | 30% |
Everything from 100 mesh up through 500 mesh lives in our filter grade wire cloth collection, and yes, we cut all of it to size.
Market Grade vs. Mill Grade
You'll see these two terms on quotes and spec sheets. Both refer to the same mesh counts; the difference is wire diameter.
- Market grade is the standard commercial spec for general industrial work, with a heavier wire for its opening. The table above is market grade. It's a good balance of strength and open area.
- Mill grade uses lighter wire at the same count, which gives a larger opening and more open area. The name is usually traced to the flour milling trade, where throughput mattered more than abrasion resistance.
Practical takeaway: if your drawing just says "100 mesh," the grade changes the opening you'll actually get. When particle size matters, spec the wire diameter or the opening explicitly, or tell us what the mesh needs to do and we'll sort out the grade for you.
When to Spec by Micron, When to Spec by Mesh
Use mesh count plus wire diameter when you're matching an existing screen, buying general-purpose mesh, or working from a drawing that calls it out that way. It's the native language of woven wire cloth, and together the two numbers fully define the product.
Use microns when the job is defined by particle size: filtering a liquid to a target rating, sizing a powder, protecting a nozzle or pump from grit above a certain size. Tell us the micron target and whether you need to stop particles at that size or pass them, and we'll come back with the weave that does it. Above roughly 325 mesh, plain square weaves run out of room and specs shift toward twill and specialty filter weaves, which is exactly the territory where speccing by micron beats speccing by count.
One caution: a woven mesh micron rating describes the geometric opening, not a certified filtration performance. Real-world retention depends on particle shape, flow, and cake buildup. For most industrial straining that distinction is academic; for critical filtration, test with actual material first. That's one of the reasons we mail out free swatches.
What About Perforated and Expanded Metal?
Mesh count is a woven-cloth concept. Perforated metal is specified by hole diameter and center-to-center spacing, and expanded metal by its diamond dimensions and strand size. Open area still applies to both, and it's often the number that decides between materials. If you're not sure which product family fits the job, the Mesh Finder is a quick way to narrow it down.
Frequently Asked Questions
Is a higher mesh number finer or coarser?
Finer. Mesh count is openings per inch, so more openings packed into the same inch means each opening is smaller. A 200 mesh screen is much finer than a 20 mesh screen. The pattern runs the same direction with wire gauge numbers, where a higher gauge means thinner wire, but the two scales aren't related, and mixing them up is a common ordering mistake. When in doubt, ask for the opening in decimal inches or microns.
How do I convert mesh size to microns?
Find the opening in inches using opening = (1 ÷ mesh count) − wire diameter, then multiply by 25,400. You need the wire diameter to do it properly; mesh count alone isn't enough. For standard commercial specs, our mesh-to-micron chart has the common counts already worked out.
What micron is 100 mesh?
In the standard market grade spec (.0045" wire), 100 mesh has a .0055" opening, which is about 140 microns. Woven with heavier or lighter wire, the same 100 mesh count can land meaningfully above or below that, so confirm the wire diameter if the micron number matters for your application.
Can two screens with the same mesh count have different opening sizes?
Yes, and it happens all the time. The same count woven with different wire diameters produces different openings, different open areas, and different strength. That's the whole reason a complete mesh spec lists both count and wire diameter. If you have an existing screen to match, measure the wire with calipers or mail us a swatch and we'll identify it.
Still not sure what to spec? That's what the phone is for. Call us at (510) 887-8787, or request a quote with whatever information you have, even if it's just "the holes need to be about this big." We've been cutting wire cloth to size in Hayward, California since 1938, and if you'd rather check the mesh in your hands before you buy, we'll put free samples in the mail.