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. 170 test sieve (ASTM E11) has a nominal opening of 90 µm.
| Opening (microns) | 90 µm |
| Opening (millimeters) | 0.09 mm |
| Opening (inches) | 0.0035 in |
| US standard sieve | No. 170 |
| Tyler equivalent | 170 mesh |
| Pitch (wire center to center) | 153 µm |
| Typical wire diameter | 0.063 mm |
| Approx. open area | 35% |
A 90 µm opening falls within the very fine sand (62.5 µm–125 µm) class of the Wentworth grain-size scale. Comparing grain size with the nominal opening only: silt and finer would pass; fine sand and coarser would be retained; very fine sand is split at about 90 µm. Real sieving also depends on particle shape, sieving time and the opening tolerance of the cloth.
These applications commonly use a 170 mesh count or an opening near 90 µm:
100 µm in-tank strainer; 70–100 µm pre-pump
In-tank stainless strainers rated 100 µm protect the pump from debris; guidance for pre-pump filtration on carbureted systems is about 70–100 µm. Injector protection needs a finer post-pump filter.
Ranges show common practice with sources on the mesh size by application page — always check your equipment maker's recommendation.
The name "170 mesh" suggests 170 openings per inch, i.e. a pitch of 25,400 ÷ 170 = 149.4 µm. Standard test sieves, however, are defined by their opening, not by the count: a 90 µm opening woven with the typical 0.063 mm wire gives a real pitch of 90 + 63 = 153 µm, which is about 166 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 |
|---|---|---|---|
| 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 |
| 200 mesh | 75 | 0.075 | 0.003 |
| 230 mesh | 63 | 0.063 | 0.0025 |
| 250 mesh | 63 | 0.063 | 0.0025 |
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.
170 mesh is 90 µm, which is 0.09 mm or 0.0035 inches.
In a simplified comparison with the nominal opening, particles smaller than about 90 µm can pass a 170 mesh screen. A 90 µm opening falls within the very fine sand (62.5 µm–125 µm) class of the Wentworth grain-size scale. Comparing grain size with the nominal opening only: silt and finer would pass; fine sand and coarser would be retained; very fine sand is split at about 90 µm. Real sieving also depends on particle shape, sieving time and the opening tolerance of the cloth.
With a typical 0.063 mm wire, 170 mesh has roughly 35% open area. Thicker wire lowers the open area and the opening size.