Mesh to Micron Converter
Enter a mesh number to get the exact ASTM E11 sieve opening in microns, millimeters, and inches. Switch to reverse mode to convert microns back to the nearest standard mesh size. The built-in reference table covers all standard U.S. mesh sizes from 3.5 mesh (5,600 microns) to 635 mesh (20 microns).
What is mesh size?
Mesh size is the number of openings per linear inch in a wire-cloth sieve or screen. A 200-mesh sieve has 200 openings across each inch of its surface, so each opening is much smaller than those in a 10-mesh sieve, which has only 10 openings per inch. Because the wire that forms the grid takes up space, the actual opening (the gap particles can pass through) is always smaller than 1/mesh inch. The relationship between mesh number and opening size is defined by standards, most commonly ASTM E11 in the United States, which specifies both the nominal opening and the wire diameter for each standard mesh size.
How mesh size converts to microns
The ASTM E11 standard lists the nominal sieve opening for each mesh number. Because wire diameter varies between mesh sizes, there is no single universal formula that gives exact results for all sizes. A widely used approximation is: opening (microns) = 25,400 / mesh, which comes from the fact that one inch equals 25,400 micrometers and assumes the wire takes up no space. This formula works reasonably well for coarser sieves but overestimates the opening for finer sieves because fine-mesh wire takes up a larger proportion of the pitch. For precise work, always use the ASTM lookup table rather than the formula. This calculator uses the standard ASTM E11 table for all listed mesh sizes and falls back to the theoretical formula only when an unlisted mesh number is entered.
Reverse conversion: microns to mesh
When you know the particle size in microns and need to find the right sieve, the reverse conversion finds the nearest ASTM E11 standard mesh size. Because mesh sizes are not evenly spaced in microns (they follow a roughly geometric progression, each step about 20-25% smaller than the previous one), your target size may not fall exactly on a standard mesh opening. In that case the calculator returns the nearest standard size and shows the difference. For particle sizing work where the exact cut point matters, you may need to use two bracketing sieves rather than a single mesh.
Particle size classification by sieve opening
Industry and scientific literature use various particle size classifications based on sieve opening. Very coarse particles (above 2,000 microns, roughly 2 mm) correspond to mesh numbers 10 and coarser and include gravel, coarse sand, and large granules. Coarse powders (500 to 2,000 microns) cover mesh 12 to 35 and include coffee grounds, granulated sugar, and coarse pharmaceutical excipients. Medium powders (150 to 500 microns) span mesh 35 to 100 and include fine sand, flour, and many tablet granulations. Fine powders (45 to 150 microns) from mesh 100 to 325 include icing sugar, fine pharmaceutical powders, and many pigments. Ultrafine or sub-sieve material below 45 microns (finer than 325 mesh) passes through conventional wire-cloth sieves and requires air classification or laser diffraction to size accurately.
ASTM E11 Mesh to Micron Reference Table
| Mesh | Microns (µm) | Millimeters (mm) | Inches (in) | Size class |
|---|---|---|---|---|
| 3.5 | 5600 | 5.600 | 0.2205 | Very coarse |
| 4 | 4750 | 4.750 | 0.1870 | Very coarse |
| 5 | 4000 | 4.000 | 0.1575 | Very coarse |
| 6 | 3350 | 3.350 | 0.1319 | Very coarse |
| 7 | 2800 | 2.800 | 0.1102 | Very coarse |
| 8 | 2360 | 2.360 | 0.0929 | Very coarse |
| 10 | 2000 | 2.000 | 0.0787 | Very coarse |
| 12 | 1700 | 1.700 | 0.0669 | Coarse |
| 14 | 1400 | 1.400 | 0.0551 | Coarse |
| 16 | 1180 | 1.180 | 0.0465 | Coarse |
| 18 | 1000 | 1.000 | 0.0394 | Coarse |
| 20 | 850 | 0.850 | 0.0335 | Coarse |
| 25 | 710 | 0.710 | 0.0280 | Coarse |
| 30 | 600 | 0.600 | 0.0236 | Coarse |
| 35 | 500 | 0.500 | 0.0197 | Coarse |
| 40 | 425 | 0.425 | 0.0167 | Medium |
| 45 | 355 | 0.355 | 0.0140 | Medium |
| 50 | 300 | 0.300 | 0.0118 | Medium |
| 60 | 250 | 0.250 | 0.0098 | Medium |
| 70 | 212 | 0.212 | 0.0083 | Medium |
| 80 | 180 | 0.180 | 0.0071 | Medium |
| 100 | 150 | 0.150 | 0.0059 | Medium |
| 120 | 125 | 0.125 | 0.0049 | Fine |
| 140 | 106 | 0.106 | 0.0042 | Fine |
| 170 | 90 | 0.090 | 0.0035 | Fine |
| 200 | 75 | 0.075 | 0.0030 | Fine |
| 230 | 63 | 0.063 | 0.0025 | Fine |
| 270 | 53 | 0.053 | 0.0021 | Fine |
| 325 | 45 | 0.045 | 0.0018 | Fine |
| 400 | 38 | 0.038 | 0.0015 | Fine |
| 450 | 32 | 0.032 | 0.0012 | Ultrafine |
| 500 | 25 | 0.025 | 0.0010 | Ultrafine |
| 635 | 20 | 0.020 | 0.0008 | Ultrafine |
Nominal sieve openings per ASTM E11-22. Actual openings may vary within tolerance.
Frequently asked questions
Is there an exact formula for converting mesh to microns?
Not a universal one. The approximation microns = 25,400 / mesh treats the wire as having zero thickness, which overestimates the opening for fine sieves. ASTM E11 defines the exact nominal opening for each standard mesh size by specifying both the opening and the wire diameter, and those values are the authoritative source. This calculator uses the ASTM table for all standard mesh sizes and the approximate formula only for non-standard mesh numbers.
What is the difference between ASTM and Tyler mesh?
ASTM E11 and the older Tyler series both define mesh-to-micron relationships, but they use different mesh numbering conventions for some sizes and define slightly different wire diameters. The Tyler series is the older U.S. standard and is still widely cited in mining and minerals literature. ASTM E11 is the current primary U.S. standard and aligns closely with ISO 3310-1. This calculator uses ASTM E11 values, which match the current U.S. and international practice for most laboratory and industrial applications.
What does it mean if a particle "passes" a sieve?
A particle that passes (goes through) a sieve is smaller than the sieve opening. A particle that is retained (stays on top) is larger than the opening. In particle size analysis, a material is often described by two mesh numbers: the sieve it passes through and the sieve it is retained on, for example "passes 200 mesh, retained on 325 mesh," meaning the particles are between 45 and 75 microns.
Why does my sieve give different results than the nominal opening?
Manufacturing tolerances allow individual openings to vary slightly around the nominal size. The ASTM E11 standard specifies maximum allowable tolerances for both individual openings and the mean opening across a sieve. Additionally, worn or clogged sieves can have openings that differ significantly from the nominal value. For critical work, sieves should be periodically calibrated and certified against NIST-traceable reference materials.
What mesh size is used for pharmaceutical powders?
Pharmaceutical sieve specifications vary by product and pharmacopoeial standard. The United States Pharmacopeia (USP) uses sieve numbers that match ASTM E11 designations. Common sizes include No. 20 (850 microns) for granule sizing, No. 40 (425 microns) for coarser powders, No. 60 (250 microns) and No. 100 (150 microns) for medium powders, and No. 200 (75 microns) or No. 325 (45 microns) for fine powders. The specific mesh requirement is defined in the individual monograph or formulation specification.