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. 25 test sieve (ASTM E11) has a nominal opening of 710 µm.
| Opening (microns) | 710 µm |
| Opening (millimeters) | 0.71 mm |
| Opening (inches) | 0.028 in |
| US standard sieve | No. 25 |
| Tyler equivalent | 24 mesh |
| Pitch (wire center to center) | 1,160 µm |
| Typical wire diameter | 0.45 mm |
| Approx. open area | 37% |
A 710 µm opening falls within the coarse sand (500 µm–1 mm) class of the Wentworth grain-size scale. Comparing grain size with the nominal opening only: medium sand and finer would pass; very coarse sand and coarser would be retained; coarse sand is split at about 710 µm. Real sieving also depends on particle shape, sieving time and the opening tolerance of the cloth.
These applications commonly use a 25 mesh count or an opening near 710 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 "25 mesh" suggests 25 openings per inch, i.e. a pitch of 25,400 ÷ 25 = 1,016 µm. Standard test sieves, however, are defined by their opening, not by the count: a 710 µm opening woven with the typical 0.45 mm wire gives a real pitch of 710 + 450 = 1,160 µm, which is about 21.9 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 |
|---|---|---|---|
| 16 mesh | 1,180 | 1.18 | 0.0465 |
| 18 mesh | 1,000 | 1 | 0.0394 |
| 20 mesh | 850 | 0.85 | 0.0335 |
| 25 mesh | 710 | 0.71 | 0.028 |
| 30 mesh | 600 | 0.6 | 0.0236 |
| 35 mesh | 500 | 0.5 | 0.0197 |
| 40 mesh | 425 | 0.425 | 0.0167 |
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.
25 mesh is 710 µm, which is 0.71 mm or 0.028 inches.
In a simplified comparison with the nominal opening, particles smaller than about 710 µm can pass a 25 mesh screen. A 710 µm opening falls within the coarse sand (500 µm–1 mm) class of the Wentworth grain-size scale. Comparing grain size with the nominal opening only: medium sand and finer would pass; very coarse sand and coarser would be retained; coarse sand is split at about 710 µm. Real sieving also depends on particle shape, sieving time and the opening tolerance of the cloth.
With a typical 0.45 mm wire, 25 mesh has roughly 37% open area. Thicker wire lowers the open area and the opening size.