Home & gardenMaker spec
Micro-mesh gutter guards
e.g. 42 mesh stainless, ≈ 440 µm
Stainless micro-mesh gutter guards pass water by surface tension and hold back debris; one maker specifies 42-mesh stainless with about 440 µm openings.
Opening440 µm
01 — StandardWhat is 40 mesh in microns?
A US standard No. 40 test sieve (ASTM E11) has a nominal opening of 425 µm.
02 — Specifications40 mesh specifications
| Opening (microns) | 425 µm |
| Opening (millimeters) | 0.425 mm |
| Opening (inches) | 0.0167 in |
| US standard sieve | No. 40 |
| Tyler equivalent | 35 mesh |
| Pitch (wire center to center) | 705 µm |
| Typical wire diameter | 0.28 mm |
| Approx. open area | 36% |
03 — ApplicationsWhat is 40 mesh used for?
A 425 µm opening falls within the medium sand (250 µm–500 µm) class of the Wentworth grain-size scale. Comparing grain size with the nominal opening only: fine sand and finer would pass; coarse sand and coarser would be retained; medium sand is split at about 425 µm. Real sieving also depends on particle shape, sieving time and the opening tolerance of the cloth.
These applications commonly use a 40 mesh count or an opening near 425 µm:
Filtration & fluidsIndustry guide
Pipeline Y-strainers
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.
Mesh count range20–60 mesh
Food, drink & pharmaMaker spec
Coffee grind sifting
Sieves from 200 to 1600 µm
Coffee sifters stack interchangeable sieves between 200 and 1600 µm to isolate a target grind range.
Opening range200 µm – 1.6 mm
Ranges show common practice with sources on the mesh size by application page — always check your equipment maker's recommendation.
04 — CalculationHow the 40 mesh value is calculated
The name "40 mesh" suggests 40 openings per inch, i.e. a pitch of 25,400 ÷ 40 = 635 µm. Standard test sieves, however, are defined by their opening, not by the count: a 425 µm opening woven with the typical 0.28 mm wire gives a real pitch of 425 + 280 = 705 µm, which is about 36 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 |
|---|---|---|---|
| 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 |
| 45 mesh | 355 | 0.355 | 0.014 |
| 50 mesh | 300 | 0.3 | 0.0118 |
| 60 mesh | 250 | 0.25 | 0.0098 |
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 40 mesh?
40 mesh is 425 µm, which is 0.425 mm or 0.0167 inches.
What size particles pass through a 40 mesh screen?
In a simplified comparison with the nominal opening, particles smaller than about 425 µm can pass a 40 mesh screen. A 425 µm opening falls within the medium sand (250 µm–500 µm) class of the Wentworth grain-size scale. Comparing grain size with the nominal opening only: fine sand and finer would pass; coarse sand and coarser would be retained; medium sand is split at about 425 µm. Real sieving also depends on particle shape, sieving time and the opening tolerance of the cloth.
What is the open area of 40 mesh?
With a typical 0.28 mm wire, 40 mesh has roughly 36% open area. Thicker wire lowers the open area and the opening size.