Mesh Size Converter

Mesh size describes the number of openings per linear inch in a screen or sieve. A higher mesh number means smaller openings and finer particle size.

How mesh size works: A 100-mesh screen has 100 openings per inch. The pitch, the distance from one wire to the next, is therefore 25,400 / 100 = 254 microns. But the wire itself occupies part of that pitch, so the hole is smaller than the pitch:

opening = (25,400 / mesh) - wire diameter

For a standard 100-mesh sieve the wire is about 104 microns, leaving a 150 micron hole. That is why mesh number alone never gives an exact opening: change the wire gauge and the same mesh count passes a different particle. Sieves sold to a published standard fix the wire diameter as well as the count, which is what makes the tables below meaningful.

Two number sets are in circulation, and this is the usual source of confusion. The current ASTM E11 series (also ISO 3310) uses tidy rounded openings. Older US Standard charts, still printed on plenty of supplier websites, carry values one to three percent different. Neither is wrong; they are different vintages of the same series, renumbered when the standard moved onto the ISO preferred-number progression. Specify against ASTM E11 unless a drawing tells you otherwise.

Common applications by mesh size:

• 4-10 mesh: Gravel screening, coarse aggregate
• 10-40 mesh: Sand, sugar, salt, grain processing
• 40-100 mesh: Flour, fine sand, ceramic powders
• 100-200 mesh: Industrial powders, pigments, pharmaceutical ingredients
• 200-400 mesh: Extremely fine powders, specialty chemicals

Practical tips:

• When filtering liquids, choose a mesh fine enough to catch the target particles but coarse enough to maintain flow rate.
• Mesh screens can clog quickly with particles near the opening size, so use a mesh 20-30% finer than the smallest particle you want to pass through.
• For 3D printing powder, typical mesh size is 200-400 mesh (38-75 microns).

A useful anchor: the sand and silt boundary sits on a 230 sieve. Geologists split sand from silt at 62.5 microns, and the standard No. 230 sieve opens at 63. So anything passing a 230 is silt or clay by definition, and anything held on it is sand. Human hair is around 70 microns across, which is roughly the same line, so if a particle is visibly grit rather than dust it is sand.

A few more sizes worth carrying in your head: beach sand runs 100 to 500 microns, table salt about 300 to 500, wheat flour 50 to 150, Portland cement 10 to 50, and airborne pollen 10 to 100. Cement fineness is actually specified as the percentage retained on a No. 325 sieve, which is 45 microns, so most of a bag of cement passes it.

Mesh count is not the same thing as filtration rating, and this catches people out when buying filter screens. A mesh figure describes the hole between the wires; a micron rating on a filter usually describes the smallest particle the filter is guaranteed to stop, which depends on the weave as well as the opening. A twilled or Dutch-weave cloth has openings that are not square holes at all, so its mesh count and its micron rating are only loosely related. Read the micron figure on a filter and the mesh figure on a sieve.

One practical note on flow. Halving the opening does not halve the flow through a screen, it cuts it far more, because the open area falls with the square while the wires get proportionally thicker. A 400 mesh screen typically has around 35 percent open area against 60 percent or more for a coarse one, so an over-fine screen chosen “to be safe” can strangle a process that a slightly coarser one would have handled with room to spare.