Enter a mesh or sieve number (40 mesh, No. 200), an opening (75 µm, 0.25 mm) or a mesh count with its wire diameter (40 mesh, wire 0.25 mm). Below, an offered opening can be checked against the one wanted.
On the aperture alone: the material, the wire diameter, the open area and the basket dimensions are checked separately.
A strainer basket says 40 mesh, a filter data sheet 150 µm, a drawing No. 200. A US standard sieve number to ASTM E11 names a fixed nominal aperture, the same as that of the matching ISO 3310-1 test sieve: No. 40 is 425 µm, No. 200 is 75 µm. Enter a mesh or sieve number, or an opening in µm or mm, and the converter gives the sieve number and aperture, draws the series on a logarithmic scale, names the sieves either side, checks an offered screen and writes an RFQ line.
On a strainer basket or a filter cloth, “mesh” often means wires per inch, and the opening then depends on the wire diameter: aperture = 25.4 mm / mesh − wire diameter. Only on a standard test sieve is the aperture of a sieve number fixed; for a strainer screen the maker’s opening size governs. Give the wire diameter and the converter works the opening out. The micron rating of a filter element is a different measure, explained by the oil cleanliness code reader.
ASTM E11 numbers the US standard test sieves from No. 4, 4.75 mm, to No. 635, 20 µm. Each number names a nominal aperture of the ISO 565 / ISO 3310-1 series, so No. 40 and the 425 µm ISO test sieve have the same aperture. The table below gives every number.
On a strainer basket liner or a filter cloth, mesh is usually the number of wires per inch. The pitch is 25.4 mm divided by the mesh and the opening is the pitch less the wire diameter, so two 40 mesh screens with 0.25 mm and 0.30 mm wire have openings of 0.385 mm and 0.335 mm.
Many strainer baskets are made of perforated plate, specified by hole diameter and pitch, sometimes with a mesh liner inside. There is no mesh number to convert: ask the strainer maker for the opening in mm and give it in the request with the basket dimensions.
| Sieve number | Aperture, µm | Aperture, mm |
|---|---|---|
| No. 4 | 4750 | 4.75 |
| No. 5 | 4000 | 4.00 |
| No. 6 | 3350 | 3.35 |
| No. 7 | 2800 | 2.80 |
| No. 8 | 2360 | 2.36 |
| No. 10 | 2000 | 2.00 |
| No. 12 | 1700 | 1.70 |
| No. 14 | 1400 | 1.40 |
| No. 16 | 1180 | 1.18 |
| No. 18 | 1000 | 1.00 |
| No. 20 | 850 | 0.850 |
| No. 25 | 710 | 0.710 |
| No. 30 | 600 | 0.600 |
| No. 35 | 500 | 0.500 |
| No. 40 | 425 | 0.425 |
| No. 45 | 355 | 0.355 |
| No. 50 | 300 | 0.300 |
| No. 60 | 250 | 0.250 |
| No. 70 | 212 | 0.212 |
| No. 80 | 180 | 0.180 |
| No. 100 | 150 | 0.150 |
| No. 120 | 125 | 0.125 |
| No. 140 | 106 | 0.106 |
| No. 170 | 90 | 0.090 |
| No. 200 | 75 | 0.075 |
| No. 230 | 63 | 0.063 |
| No. 270 | 53 | 0.053 |
| No. 325 | 45 | 0.045 |
| No. 400 | 38 | 0.038 |
| No. 450 | 32 | 0.032 |
| No. 500 | 25 | 0.025 |
| No. 635 | 20 | 0.020 |
Each aperture is in at least two independent sieve tables aligned with ISO 3310-1, and they agree on every number. Left out: No. 3-1/2 and the inch designations coarser than No. 4 (the table runs over whole sieve numbers from No. 4); the nominal wire diameters of the test sieves (only one source gave them); the mesh numbers of other series used by some makers (one source); the figures of some commercial charts that are not apertures of the ISO series, such as 0.841 mm for No. 20 or 74 µm for No. 200. The formula aperture = 25.4 mm / mesh − wire diameter, for a square weave, is as two wire cloth makers’ references give it.
Apertures from the sieve charts of a test sieve maker and a wire cloth maker, an encyclopedia table, an extract of the ASTM E11 table and a materials testing body; the formula from the references of two wire cloth makers. Every aperture on this page is in at least two of them.
On a standard test sieve, No. 40 to ASTM E11 has a nominal aperture of 425 µm (0.425 mm), the same aperture as the 425 µm test sieve of ISO 3310-1. On a strainer basket or a filter cloth, 40 mesh usually means 40 wires per inch, and the opening then depends on the wire diameter: with 0.25 mm wire it is 25.4 mm / 40 − 0.25 mm = 0.385 mm, or 385 µm.
Only roughly. On a test sieve the number names a fixed nominal aperture: No. 200 is 75 µm, whatever wire the cloth is woven from. On a woven screen that is not a test sieve, a mesh count is a count of wires per inch, and two screens of the same mesh with different wires have different openings.
Some commercial charts give figures such as 0.841 mm for No. 20, 0.149 mm for No. 100 or 74 µm for No. 200 that are not apertures of the ISO 565 / ISO 3310-1 series. The current ASTM E11 sieves have the ISO apertures, 850, 150 and 75 µm for those numbers, and this converter uses only the apertures that the sieve tables aligned with ISO 3310-1 agree on.
By its opening in millimetres or micrometres, and whether it is a perforated plate with a hole size or a woven mesh, with the wire diameter if known. Add the material, the strainer maker and size, the basket or element dimensions and the quantity. A mesh count alone does not fix the opening.
Not necessarily. As a general rule a finer screen holds back smaller particles but, other things being equal, adds pressure drop and fills up sooner, so it needs cleaning more often. The opening is chosen for the equipment the strainer protects; the strainer or equipment maker’s figure governs.
Not necessarily. A woven screen has an opening that can be measured: No. 500 has a 25 µm aperture. A filter element’s micron rating describes how well it captures particles of that size in a test, often given as a beta ratio; the oil cleanliness code reader explains beta ratios.
A mesh number is not a screen. Add the opening, the material, the strainer maker and size and a photograph of the old basket or the strainer nameplate, and Vessel Core checks them before an offer goes back.
