Grit Rating:

A number that indicates the grit of sandpaper or another abrasive product. The lower the number is, the coarser the grit. Traditionally, the grit rating corresponds to the size of the wire mesh used to sift the abrasive particles. For example, medium-grade sandpaper with a grit rating of 120 consists of particles that could pass through mesh with 120 wires in both directions in a square inch.