Quick answer
400 mesh ≈ 0.037 mm opening
Handbook references cite roughly 0.037 millimeters (37 µm / 0.0015 inches) as the nominal aperture for 400 mesh woven cloth.
Nominal opening
- Mesh
- 400
- Millimeters (mm)
- 0.037
- Microns (µm)
- 37
- inch
- 0.0015
Ultra-fine polishing
Millimeter openings remain nominal
Digital micrometers and SEM inspections routinely diverge from handbook millimeter rounding — especially past 400 mesh.
Nearby mesh comparison
| Mesh | µm | mm | Link |
|---|---|---|---|
| 400 | 37 | 0.037 | Micron-focused page |
| 325 | 44 | 0.044 | Micron-focused page |
| 500 | 25 | 0.025 | Micron-focused page |
Try the calculators
Switch between mesh ↔ micron modes instantly when estimating powders or filtration stacks.
Why mesh ≠ pure math
Opening width equals nominal spacing minus wire thickness — charts freeze mid-process assumptions so engineers can communicate faster.
Typical applications
Metal powders, ceramics, toner, pigments, and hydraulic filtration specs routinely cite millimeter-friendly openings alongside micron targets.
People also ask
- Why show mm if microns dominate?
- Mechanical drawings and legacy ERP templates still prefer millimeters — mm keeps spreadsheets concise.
- Can I specify only millimeters on a PO?
- Pair mm openings with mesh counts plus supplier tolerance bands to avoid ambiguity.
- Does ASTM publish mm columns?
- Modern ASTM listings emphasize micron aperture — mm derives from dividing microns by 1000.
- ASTM vs ISO — still approximate?
- Yes — refer to MeshToMicron sieve standards primer for citations.
- Should QA rely on these mm figures?
- Use them as intake estimates — retained mass tests settle disputes.
Millimeter rounding can hide microns of error on fine sieves — escalate to microscopy if needed.