Knots Per Square Inch (KPSI) is exactly that, a measure of how many individual knots are in a typical square inch of an Area Rug. Generally, the higher the KPSI, the more valuable the Area Rug is.

As the density of knots goes up (high KPSI), so does the rug's durability, labor time / costs, material costs, weight and required craftsmanship. A high KPSI Area Rug will also feel finer to the touch and its color patterns will have crisper edges and a sharper appeal to the eye.

RugScout offers hand-made rugs that range from about 25 KPSI to well over 500 KPSI. If you buy an Area Rug with a KPSI over 150, it can get expensive. And if KPSI goes over 300, you're buying something really special! Even very small rugs (2' x 3') in the 300+ KPSI range often have estimated retail values above $2,000.

In the US, Canada and the UK, KPSI is the standard unit used. In Persia, where the hand-made rugs are typically made, the metric system is used - so they use RAJ. RAJ is the number of knots in a 7 cm row.

If you take the RAJ, divide it by 7 (to get to knots in a one cm line), multiply times 2.54 (to convert from centimeters to inches) and then square that number (to get to knots per area, versus knots per row) you'll have the equivalent knot density in KPSI. Example: 25 RAJ = 82 KPSI.