What this calculator does
Mesh number describes how many openings a sieve or screen has per linear inch: a higher mesh number means a finer screen with smaller openings. It is a count, not a direct measurement of size, so converting a mesh number into an actual opening size in microns needs a formula rather than a simple lookup.
The conversion used here, micron size approximately equal to 14,930 divided by the mesh number, is a widely cited approximation for standard woven wire mesh. It is not an exact physical law: the true opening size also depends on the wire diameter used, which varies between manufacturers and mesh standards, so a real specification sheet or mesh chart should be used wherever precision genuinely matters.
The formula
Divide 14,930 by the mesh number to estimate the opening size in microns, or divide 14,930 by a known opening size in microns to estimate the equivalent mesh number. The constant folds in the standard one-inch reference length and a typical wire diameter assumption, which is why it is only ever an approximation.
| Term | Meaning |
|---|---|
| Mesh number | The number of openings per linear inch of screen or sieve; higher numbers mean finer screens. |
| Micron (µm) | A millionth of a metre, the usual unit for describing particle size and sieve opening size. |
| Approximation | This conversion assumes a typical wire diameter for standard woven mesh; actual openings vary by wire gauge and manufacturer. |
The inputs explained
| Field | What to enter |
|---|---|
| Convert | Choose from Mesh number to microns, Microns to mesh number. |
| Mesh number (used when converting mesh to microns) | The mesh number printed on the sieve or screen, or specified for a filter or particle size. |
| Opening size (used when converting microns to mesh) (µm) | A target opening size in microns, when working out roughly which mesh number would achieve it. |
When to use it
Choosing a sieve for a target particle size
Working from a desired particle cut-off size in microns to an approximate mesh number narrows down which standard sieve to reach for, before checking a manufacturer chart for the exact specification.
Comparing sieve standards described only by mesh number
Product listings and lab equipment sometimes quote only a mesh number; converting to microns puts it on the same footing as a particle size spec given directly in microns.
Sanity-checking a supplier data sheet
If a screen is described with both a mesh number and a micron rating, this approximation gives a quick way to check the two figures are at least roughly consistent with each other.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
Approximate opening size across common mesh numbers
A range of commonly used mesh numbers and their approximate opening size.
| Mesh number | Approximate opening size |
|---|---|
| 20 | 746.50 µm |
| 40 | 373.25 µm |
| 60 | 248.83 µm |
| 100 | 149.30 µm |
| 140 | 106.64 µm |
| 200 | 74.65 µm |
| 325 | 45.94 µm |
Questions
Why is this only an approximation and not an exact conversion?
Mesh number counts openings per inch, but the actual size of each opening also depends on how thick the wire is. Two screens with the same mesh number but different wire diameters will have slightly different true opening sizes, which this single formula cannot capture.
What should I use if I need an exact opening size?
Check the manufacturer specification sheet or a recognised mesh-to-micron reference chart for the specific mesh standard and wire gauge in question, since those account for the actual wire diameter rather than a general approximation.
Does a higher mesh number always mean a smaller opening?
Yes, that relationship always holds. A higher mesh number means more openings packed into the same linear inch, which necessarily makes each individual opening smaller.
Is this the same formula used for all mesh standards worldwide?
No. Different standards (such as US mesh, Tyler mesh and ISO sieve sizes) can assign slightly different opening sizes to a similarly numbered mesh. This approximation is a general rule of thumb rather than a specific national or international standard.
For everyday length conversions, see the site’s general conversion tools, or the percentage calculator for working out particle-size retained or passed as a percentage of a sample.