Why a mesh spec is a system, not a single number
A wire mesh specification is rarely one figure. It is a small set of interdependent values that together describe a screen: how many wires sit in an inch, how wide the clear gaps are, how thick those wires are, what fraction of the surface is open, and how the wires interlace. Quote any one value in isolation and you have only described part of the product.
The values are linked by geometry. For a square plain-weave mesh, the centre-to-centre wire pitch equals one inch divided by the mesh count, and the opening is that pitch minus one wire diameter. So if you fix the mesh count and increase the wire diameter, the opening shrinks and the open area falls. Understanding this relationship is what lets you read a spec critically rather than trusting a single headline number.
Rule of thumb: opening = (25.4 / mesh count) - wire diameter, with all lengths in millimetres. This is the backbone equation that ties mesh count, wire diameter and opening together for square woven mesh.
Mesh count: wires per inch
Mesh count is the number of openings (or, equivalently, the number of wires) per linear inch, measured from the centre of one wire to a point one inch away. A 100 mesh screen has 100 wires per inch in each direction. A higher mesh count means more, finer wires packed into the same inch, and therefore smaller openings.
Mesh count alone does not tell you the opening size, because two screens of the same mesh count can use different wire diameters. A 30 mesh screen woven with a heavy wire has a noticeably smaller opening than a 30 mesh screen woven with a fine wire. Always pair the mesh count with the wire diameter or the stated opening before drawing conclusions about filtration or particle retention.
- Coarse mesh: roughly 2 to 20 mesh, used for screening, guarding and aggregate sizing.
- Medium mesh: roughly 20 to 80 mesh, common for general filtration and sieving.
- Fine mesh: roughly 80 to 200 mesh and finer, used for fine filtration and particle classification.
Opening size: the clear gap that does the work
The opening (also called aperture) is the clear distance between two adjacent parallel wires. It is the dimension that actually governs what passes through and what is retained, which is why filtration and sieving are usually specified by opening rather than by mesh count. Opening is quoted in millimetres, inches or microns.
Because opening is mesh pitch minus wire diameter, a published opening is only meaningful alongside the wire diameter it was calculated from. The table below shows indicative typical openings for common mesh counts, computed from representative wire diameters. Treat these as a starting point: real mill products vary by weaver, wire tolerance and standard, so confirm the exact opening on a mill specification before you commit.
| Mesh count | Typical wire dia (mm) | Typical opening (mm) | Typical opening (micron) | Approx. open area |
|---|---|---|---|---|
| 10 | 0.90 | 1.64 | 1640 | 42% |
| 20 | 0.45 | 0.82 | 820 | 42% |
| 30 | 0.30 | 0.55 | 547 | 42% |
| 40 | 0.25 | 0.39 | 385 | 37% |
| 50 | 0.20 | 0.31 | 308 | 37% |
| 60 | 0.18 | 0.24 | 243 | 33% |
| 80 | 0.14 | 0.18 | 178 | 31% |
| 100 | 0.10 | 0.15 | 154 | 37% |
| 120 | 0.08 | 0.13 | 132 | 39% |
| 150 | 0.065 | 0.10 | 104 | 38% |
| 200 | 0.053 | 0.074 | 74 | 34% |
These openings are indicative. A different wire diameter at the same mesh count produces a different opening and open area. Never size filtration from mesh count alone; always work from the confirmed opening for the specific product.
Wire diameter and gauge: the inverse number trap
Wire diameter is the thickness of the wire used to weave the mesh, normally quoted directly in millimetres or inches. Some suppliers and older drawings instead quote a wire gauge number. The catch with gauge is that it runs inversely to diameter: a smaller gauge number means a thicker wire. An 8 gauge wire is far heavier than a 30 gauge wire.
Gauge is also not universal. Several gauge systems exist (for example imperial and American systems), and the same gauge number can correspond to slightly different diameters depending on which system is used. Because of this ambiguity, professional practice is to specify and confirm wire diameter in millimetres or inches, and to treat any gauge figure as a label that must be resolved to an actual diameter before ordering.
| Gauge | Approx. dia (mm) | Approx. dia (inch) |
|---|---|---|
| 8 | 4.064 | 0.160 |
| 10 | 3.251 | 0.128 |
| 12 | 2.642 | 0.104 |
| 14 | 2.032 | 0.080 |
| 16 | 1.626 | 0.064 |
| 18 | 1.219 | 0.048 |
| 20 | 0.914 | 0.036 |
| 22 | 0.711 | 0.028 |
| 24 | 0.559 | 0.022 |
| 26 | 0.457 | 0.018 |
| 28 | 0.376 | 0.015 |
| 30 | 0.315 | 0.012 |
Remember the inverse: lower gauge number = thicker wire. And because gauge systems differ, a gauge figure on its own is not a precise diameter. Resolve it to millimetres before you weave or buy.
Open area: how much of the screen is actually a hole
Open area is the percentage of the total mesh surface that is open space rather than wire. For square mesh it is the opening divided by the pitch, squared, expressed as a percentage. A higher open area means more flow, more throughput and less pressure drop, but usually thinner or more widely spaced wires and so a weaker, less abrasion-resistant screen.
Open area is the lever between flow and strength. When you increase wire diameter to gain durability at a fixed mesh count, you reduce the opening and the open area, and therefore the flow. When you need more flow, you either coarsen the mesh or use a thinner wire, trading away strength. Reading open area alongside opening tells you which side of that trade a given spec sits on.
Weave type: plain, twill and Dutch
Weave type describes how the warp and weft wires interlace, and it changes the mesh's strength, opening shape and flow behaviour even when the count and wire diameter are held constant.
Plain weave
Each weft wire passes alternately over and under each warp wire. This is the most common weave, giving square, uniform openings and a flat, stable screen. It is the default for general sieving, filtration and screening.
Twill weave
Each weft wire passes over two and under two warp wires. Twill lets the weaver use heavier wire at a given mesh count, or weave finer meshes than plain weave allows, at the cost of a slightly less open and less uniform aperture. It is used where strength or very fine counts are needed.
Dutch weave
Dutch weaves use different wire diameters or spacings for warp and weft so the wires pack tightly, producing very fine, tortuous filtration paths and high strength. Plain Dutch and twilled Dutch weaves are specified by their filtration rating (the size of particle retained) rather than by a simple square opening, because the apertures are not square.
Material grades: what the wire is made of
The wire material sets corrosion resistance, strength, temperature tolerance and cost. A mesh spec is incomplete without it, because two screens with identical geometry can behave completely differently in service depending on alloy.
- Stainless steels (such as the common austenitic 304 and the more corrosion-resistant 316 / 316L grades): the default for filtration, food, chemical and marine-adjacent use; 316/316L add resistance to chlorides and pitting.
- Low-carbon and galvanised steel: economical, strong, for screening, fencing and guarding where corrosion exposure is limited.
- Brass, bronze and copper: used for specific conductivity, decorative or shielding needs.
- Higher alloys and nickel-based grades: for aggressive chemical or high-temperature environments.
When a grade is quoted, confirm whether it refers to the wire alloy and whether any standard, finish or certification is implied. The grade should be stated explicitly on the specification rather than assumed from a generic 'stainless' label.
Reading a full spec end to end
Putting it together, a complete and unambiguous wire mesh specification names the mesh count, the wire diameter (resolved from any gauge), the resulting opening, the open area, the weave type, the material grade and the sheet or roll dimensions. With those in hand you can predict flow, retention and durability, and you can compare two quotes on equal terms.
- Read the mesh count to gauge fineness, but do not stop there.
- Resolve the wire diameter, converting any gauge number to millimetres and noting which gauge system was used.
- Confirm the opening, ideally from the mill figure rather than a generic table.
- Check the open area to understand the flow-versus-strength trade.
- Note the weave type, since it changes aperture shape and strength.
- Confirm the material grade and any finish.
- Convert and cross-check the numbers, then verify everything against a mill specification before ordering.
Need to move between mesh count, opening and wire diameter quickly? Use the spec converter to test how changing one value reshapes the others before you lock a specification.