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. 120 test sieve (ASTM E11) has a nominal opening of 125 µm.
| Opening (microns) | 125 µm |
| Opening (millimeters) | 0.125 mm |
| Opening (inches) | 0.0049 in |
| US standard sieve | No. 120 |
| Tyler equivalent | 115 mesh |
| Pitch (wire center to center) | 215 µm |
| Typical wire diameter | 0.09 mm |
| Approx. open area | 34% |
A 125 µm opening sits exactly on the Wentworth boundary between very fine sand and fine sand. Comparing grain size with the nominal opening only: grains up to and including 125 µm would pass; grains larger than 125 µm would be retained. Real sieving also depends on particle shape, sieving time and the opening tolerance of the cloth.
These applications commonly use a 120 mesh count or an opening near 125 µm:
At least 120 mesh; drip tape at least 155 mesh
Drip line, emitters and sprayers need at least 120 mesh filtration; drip tape needs at least 155 mesh. Follow the emitter maker for your water quality.
Medium 260 µm · fine 190 µm · extra-fine 125 µm
Cone paint strainers are sold as medium (260 µm) and fine (190 µm); extra-fine 125 µm strainers are also available.
Ranges show common practice with sources on the mesh size by application page — always check your equipment maker's recommendation.
The name "120 mesh" suggests 120 openings per inch, i.e. a pitch of 25,400 ÷ 120 = 211.7 µm. Standard test sieves, however, are defined by their opening, not by the count: a 125 µm opening woven with the typical 0.09 mm wire gives a real pitch of 125 + 90 = 215 µm, which is about 118.1 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 |
|---|---|---|---|
| 70 mesh | 212 | 0.212 | 0.0083 |
| 80 mesh | 180 | 0.18 | 0.0071 |
| 100 mesh | 150 | 0.15 | 0.0059 |
| 120 mesh | 125 | 0.125 | 0.0049 |
| 140 mesh | 106 | 0.106 | 0.0042 |
| 150 mesh | 106 | 0.106 | 0.0042 |
| 170 mesh | 90 | 0.09 | 0.0035 |
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.
120 mesh is 125 µm, which is 0.125 mm or 0.0049 inches.
In a simplified comparison with the nominal opening, particles smaller than about 125 µm can pass a 120 mesh screen. A 125 µm opening sits exactly on the Wentworth boundary between very fine sand and fine sand. Comparing grain size with the nominal opening only: grains up to and including 125 µm would pass; grains larger than 125 µm would be retained. Real sieving also depends on particle shape, sieving time and the opening tolerance of the cloth.
With a typical 0.09 mm wire, 120 mesh has roughly 34% open area. Thicker wire lowers the open area and the opening size.