A very common Google PAA question is: “How do you convert mesh size to microns, and should I rely on mesh or particle size?”
The short answer is: mesh size is approximate, while micron-based particle size is more accurate.

Mesh size indicates the number of sieve openings per inch, but calcium carbonate particles are not perfectly spherical, and ultra-fine powders cannot be accurately measured by sieving alone. For this reason, mesh-to-micron conversion is always an estimation.

As a general industry reference:

• 325 mesh is approximately 45 microns

• 400 mesh is around 38 microns

• 800 mesh is roughly 18–23 microns

• 1500–2500 mesh typically corresponds to 5–10 microns

• 3000 mesh and finer usually means particles below 5 microns

However, these values can vary depending on grinding method, particle shape, and classification process.

For professional and international markets, laser particle size distribution is the preferred method. The most commonly used indicators are:

• D50: the median particle size (50% of particles are smaller than this value)

• D90 or D97: the upper size limit, indicating powder uniformity

For example, a product described as “3000 mesh calcium carbonate” may also be specified as D50 = 2.5 μm, D97 ≤ 8 μm, which provides much clearer information for formulators.

In practical terms:

• Mesh size is still useful for basic classification and domestic communication.

• Micron-based data (D50/D97) is essential for coatings, plastics, paper coating, and export markets.

If accuracy, consistency, and formulation performance matter, particle size distribution should always be prioritized over mesh alone.