Sandpaper grit size refers to the size of the particles of abrading materials embedded in the sandpaper. There are a number of different standards that have been established for grit size. These standards establish not only the average grit size, but also the allowable variation from the average. The two most common are the United States CAMI (Coated Abrasive Manufacturers Institute, now part of the Unified Abrasives Manufacturers' Association) and the European FEPA (Federation of European Producers of Abrasives) "P" grade. The FEPA system is the same as the ISO 6344 standard. An additional measuring system used in sandpaper grits is micron grade (generally used for very fine grits). Also, cheaper sandpapers sometimes are sold with nomenclature such as "Coarse", "Medium" and "Fine", but it is never clear to what standards these names refer.
FEPA Grading: The majority of coated abrasives manufactured today use the FEPA standard (Federation of European Producers of Abrasives), otherwise known in the industry as “P” grading. Abrasives in the P scale are graded to higher tolerances than CAMI graded abrasives.
CAMI Grading: This grading standard is used exclusively by US manufacturers of coated abrasives, and is overseen by the Coated Abrasive Manufacturer’s Institute and the American National Standards Institute (ANSI). The CAMI-scale tolerates a wider range of grain sizes within the definition of the grit.
Micron Grading: This refers to an abrasive particle’s actual diameter in micrometers, rather than the total number of abrasive grains that can pass through a linear inch in a screen or mesh (as the FEPA and CAMI grading system use). Micron grading has the tightest tolerances for grain size and in abrasives are typically used only in fine grits, when a stray scratch from an outsized grain would make a substantial difference to the finish.
If you have additional questions about sandpaper grits and how they compare to one another, please give Abrasive Resource a call at 800-814-7358 and be sure to download our grit comparsion chart at abrasiveresource.comAbrasive Resource is your source for the finest abrasive products!