This comparison table is somewhat inaccurate. But maybe it can at least give a few clues. Unfortunately, there are no formulas for the conversion, so you always seem to have to rely on tables. And unfortunately, the abrasive media often do not even mention the standard according to which the grit is specified.
Mesh is the number of meshes for sieving abrasive grains per square inch (i.e., an American standard).
Micron is a thousandth of a millimeter and here a measure of the size of the abrasive grains.
JIS means the grit size measured in the Japanese standard. So, at least for the Japanese stones, we can assume that they are described according to this standard.
FEPA-F applies to grinding stones, FEPA-P for abrasive paper. Both are European standards.
DMT is a large manufacturer of diamond "stones".
Mesh | Micron | JIS | FEPA-F | FEPA-P | Name |
---|---|---|---|---|---|
120 | 125 | 120 | 120 | 120 | DMT: extra-extra-coarse |
220 | 60 | 240 | 220 | 240 | DMT: extra-coarse |
325 | 44 | 330 | 290 | 280 | DMT: coarse |
600 | 22 | 600 | 400 | 700 | DMT: fine |
1200 | 9 | 1200 | 600 | 1500 | DMT: extra-fine |
4000 | 6 | 2000 | 800 | 2200 | unknown |
8000 | 3 | 4000 | 1200 | 5000 | DMT: extra-extra-fine |
A few sources on this inexhaustible topic: