Persian knot, Turkish knot, and Tibetan knot are popular rug knotting techniques. The knots per square inch (KPSI) indicate the intricacy of the rug. To get the KPSI of a rug, turn it over and count the number of knots from its back, in a single horizontal inch and a vertical inch. Multiply the numbers to get the KPSI. Measure Knot Per Square Inch to know more about measurement of rugs knot.