Grit Comparison Chart
There are three commonly used grading scales when it comes to the grit of sandpaper. In the U.S., it’s the CAMI scale; in Europe it’s called the FEPA or the P scale, and finally the Micron scale (µ). There is also a Japanese scale, but that is not one of the more commonly used scales here in the U.S. The CAMI and P scales refer to the particles per square inch, and the scale number gets larger as the particle gets smaller. The Micron scale refers to the size of the particle, so the number gets larger as the particle gets larger. For example, a 150 micron particle is larger than a 15-micron particle, while the particle on a 150 grit sandpaper is smaller than the particle on a 15 grit sandpaper. The U.S. and European scales are pretty much the same until you reach 240 grit. After this point they diverge to where 400 grit U.S. = P800.
The major difference between the scales is the tolerance for variation in grain size within a grit. The P and Micron scales have a much tighter tolerance than the U.S. CAMI scale. The Micron scale has the tightest tolerance. The tighter tolerance means a more consistent cut and fewer stray scratches from oversized particles. P and Micron scale papers are consistent enough for sanding finish- es/paint. Micron scale papers are a must for sanding solid surface materials. They also provide the most uniform of textures on wood and finishes. The table on the left compares the different grades.