01 — StandardWhat is 325 mesh in microns?
A US standard No. 325 test sieve (ASTM E11) has a nominal opening of 45 µm.
02 — Specifications325 mesh specifications
| Opening (microns) | 45 µm |
| Opening (millimeters) | 0.045 mm |
| Opening (inches) | 0.0018 in |
| US standard sieve | No. 325 |
| Tyler equivalent | 325 mesh |
| Pitch (wire center to center) | 77 µm |
| Typical wire diameter | 0.032 mm |
| Approx. open area | 34% |
03 — ApplicationsWhat is 325 mesh used for?
A 45 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 45 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 325 mesh value is calculated
The name "325 mesh" suggests 325 openings per inch, i.e. a pitch of 25,400 ÷ 325 = 78.2 µm. Standard test sieves, however, are defined by their opening, not by the count: a 45 µm opening woven with the typical 0.032 mm wire gives a real pitch of 45 + 32 = 77 µm, which is about 329.9 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.
05 — CompareNearby mesh sizes
| Mesh | Microns (µm) | Millimeters | Inches |
|---|---|---|---|
| 250 mesh | 63 | 0.063 | 0.0025 |
| 270 mesh | 53 | 0.053 | 0.0021 |
| 300 mesh | ≈ 51 | 0.051 | 0.002 |
| 325 mesh | 45 | 0.045 | 0.0018 |
| 400 mesh | 38 | 0.038 | 0.0015 |
| 450 mesh | 32 | 0.032 | 0.0013 |
| 500 mesh | 25 | 0.025 | 0.001 |
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 325 mesh?
325 mesh is 45 µm, which is 0.045 mm or 0.0018 inches.
What size particles pass through a 325 mesh screen?
In a simplified comparison with the nominal opening, particles smaller than about 45 µm can pass a 325 mesh screen. A 45 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 45 µm. Real sieving also depends on particle shape, sieving time and the opening tolerance of the cloth.
What is the open area of 325 mesh?
With a typical 0.032 mm wire, 325 mesh has roughly 34% open area. Thicker wire lowers the open area and the opening size.