01 — StandardWhat is 635 mesh in microns?
A US standard No. 635 test sieve (ASTM E11) has a nominal opening of 20 µm.
02 — Specifications635 mesh specifications
| Opening (microns) | 20 µm |
| Opening (millimeters) | 0.02 mm |
| Opening (inches) | 0.0008 in |
| US standard sieve | No. 635 |
| Tyler equivalent | 635 mesh |
| Pitch (wire center to center) | 40 µm |
| Typical wire diameter | 0.02 mm |
| Approx. open area | 25% |
03 — ApplicationsWhat is 635 mesh used for?
A 20 µm opening falls within the silt (3.9 µm–62.5 µm) class of the Wentworth grain-size scale. Comparing grain size with the nominal opening only: very fine sand and coarser would be retained; silt is split at about 20 µm. Real sieving also depends on particle shape, sieving time and the opening tolerance of the cloth.
We have no sourced application data for openings this size yet.
Ranges show common practice with sources on the mesh size by application page — always check your equipment maker's recommendation.
04 — CalculationHow the 635 mesh value is calculated
The name "635 mesh" suggests 635 openings per inch, i.e. a pitch of 25,400 ÷ 635 = 40 µm. Standard test sieves, however, are defined by their opening, not by the count: a 20 µm opening woven with the typical 0.02 mm wire gives a real pitch of 20 + 20 = 40 µm, which is about 635 wires per inch. That is why mesh numbers and micron values never line up perfectly — and why this site uses the ASTM E11 opening as the answer.
05 — CompareNearby mesh sizes
| Mesh | Microns (µm) | Millimeters | Inches |
|---|---|---|---|
| 450 mesh | 32 | 0.032 | 0.0013 |
| 500 mesh | 25 | 0.025 | 0.001 |
| 600 mesh | ≈ 21.2 | 0.021 | 0.0008 |
| 635 mesh | 20 | 0.02 | 0.0008 |
| 800 mesh | ≈ 15.9 | 0.016 | 0.0006 |
| 1000 mesh | ≈ 12.7 | 0.013 | 0.0005 |
Values are ASTM E11 nominal openings (Tyler equivalents for 150 and 250 mesh). Italic ≈ values are estimates for non-standard mesh counts, calculated from the mesh count and an assumed wire diameter (interpolated between ASTM E11 sieves, or extrapolated beyond No. 635). Wire values are ASTM E11 typical wire for standard sizes.
06 — FAQFrequently asked questions
How many microns is 635 mesh?
635 mesh is 20 µm, which is 0.02 mm or 0.0008 inches.
What size particles pass through a 635 mesh screen?
In a simplified comparison with the nominal opening, particles smaller than about 20 µm can pass a 635 mesh screen. A 20 µm opening falls within the silt (3.9 µm–62.5 µm) class of the Wentworth grain-size scale. Comparing grain size with the nominal opening only: very fine sand and coarser would be retained; silt is split at about 20 µm. Real sieving also depends on particle shape, sieving time and the opening tolerance of the cloth.
What is the open area of 635 mesh?
With a typical 0.02 mm wire, 635 mesh has roughly 25% open area. Thicker wire lowers the open area and the opening size.