This chart compares sandpaper grits using three different grading systems: 1) Coated Abrasives manufacturer’s Institute (CAMI), 2) Federation of European Producers Association (FEPA), and 3) the “0” or “ought” grade system. CAMI and FEPA are the two most common grading systems in use today. CAMI is used primarily in North America whereas FEPA is used in Europe and many other parts of the world. The “ought” system is an older grading system that is seldom used anymore but included here for sentimental reasons.
Sandpaper is labeled on the back with the grit size. If there is a “P” in front of the grit number (ex: P180), the grading system is FEPA. If there is no P prefix, it is CAMI. (There are other standards such as JIS but it is rarely used outside of Japan).
The CAMI and FEPA scratch patterns are similar for the coarser grits up to 220 grit or so. Above this, FEPA graded sandpaper becomes increasingly coarser than CAMI graded paper for a given grit size. In addition, CAMI is less stringent than FEPA in that it tolerates a wider range of particle sizes for a given grit grade. This is not a big deal for coarser grits because a finished surface is not the goal and hence CAMI is still used for grades coarser than 80 grit by most major abrasive manufacturers. On the other hand, because FEPA does have a tighter tolerance for particle size (= more consistent scratch pattern), some woodworkers prefer FEPA graded paper for fine finish sanding tasks.