Magnified schematic — the wire-to-opening ratio is true to scale; very thin lines are drawn at a minimum visible width.
A US standard No. 45 test sieve (ASTM E11) has a nominal opening of 355 µm.
| Opening (microns) | 355 µm |
| Opening (millimeters) | 0.355 mm |
| Opening (inches) | 0.014 in |
| US standard sieve | No. 45 |
| Tyler equivalent | 42 mesh |
| Pitch (wire center to center) | 579 µm |
| Typical wire diameter | 0.224 mm |
| Approx. open area | 38% |
A 355 µm opening falls within the medium sand (250 µm–500 µm) class of the Wentworth grain-size scale. Comparing grain size with the nominal opening only: fine sand and finer would pass; coarse sand and coarser would be retained; medium sand is split at about 355 µm. Real sieving also depends on particle shape, sieving time and the opening tolerance of the cloth.
These applications commonly use a 45 mesh count or an opening near 355 µm:
Water 20–40 mesh · steam 40–60 mesh
A common recommendation: 20–40 mesh for chilled and city water lines, 40–60 mesh for steam (very fine mesh is eroded by high-velocity steam). Follow the equipment maker for your service.
Sieves from 200 to 1600 µm
Coffee sifters stack interchangeable sieves between 200 and 1600 µm to isolate a target grind range.
Ranges show common practice with sources on the mesh size by application page — always check your equipment maker's recommendation.
The name "45 mesh" suggests 45 openings per inch, i.e. a pitch of 25,400 ÷ 45 = 564.4 µm. Standard test sieves, however, are defined by their opening, not by the count: a 355 µm opening woven with the typical 0.224 mm wire gives a real pitch of 355 + 224 = 579 µm, which is about 43.9 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.
| Mesh | Microns (µm) | Millimeters | Inches |
|---|---|---|---|
| 30 mesh | 600 | 0.6 | 0.0236 |
| 35 mesh | 500 | 0.5 | 0.0197 |
| 40 mesh | 425 | 0.425 | 0.0167 |
| 45 mesh | 355 | 0.355 | 0.014 |
| 50 mesh | 300 | 0.3 | 0.0118 |
| 60 mesh | 250 | 0.25 | 0.0098 |
| 70 mesh | 212 | 0.212 | 0.0083 |
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.
45 mesh is 355 µm, which is 0.355 mm or 0.014 inches.
In a simplified comparison with the nominal opening, particles smaller than about 355 µm can pass a 45 mesh screen. A 355 µm opening falls within the medium sand (250 µm–500 µm) class of the Wentworth grain-size scale. Comparing grain size with the nominal opening only: fine sand and finer would pass; coarse sand and coarser would be retained; medium sand is split at about 355 µm. Real sieving also depends on particle shape, sieving time and the opening tolerance of the cloth.
With a typical 0.224 mm wire, 45 mesh has roughly 38% open area. Thicker wire lowers the open area and the opening size.