When we talk about area rugs, whether new reproduction rugs or the antique originals on which they are based, one of the most common ways of categorizing them is by their level of fineness.
Specifically, the fineness we refer to is the fineness of weave density, with the finest rugs being those with the tightest weave density. In the West, we often express this level of weave density in terms of KPSI, or knots per square inch. In the East, the more traditional expression is in terms of RAJ, or knots per 7 centimeters. The higher the KPSI or RAJ, the finer the rug.