Quality and Number of Knots

The number of knots in a carpet is one of the key factors that determines its quality. As the number of knots increases, the design becomes sharper, in the same way that a high-resolution photo has a higher number of dots per square inch (DPS) than a standard resolution photo.
A higher number of knots also creates a stronger foundation and protects the pile.
In general, carpets with a higher number of knots are more expensive. This makes sense; more material is used, more time is taken in the weaving process, and more expert workmanship is required to ensure precision in the design. Such rugs, because they are expensive, will generally use the best quality wool, the best dye and a carefully prepared design.
It can, however, be argued that the quality of the wool and dye are more important than the number of knots. It is not unusual to see a beautiful antique carpet made with fewer knots but excellent quality wool and dye.

Knot Density

The following is an approximate guide to knot density:
• Up to 30 knots per sq. in: very coarse
• 30 — 60 knots per sq. in: coarse
• 60 — 130 knots per sq. in: medium fine
• 130 — 160 knots per sq. in: fine
• 160 - 290 knots per sq. in: very fine
• Over 290 knots per sq. in: extremely fine
Note that the thickness of the pile is not an indication of the rug's quality; more often than not the finest carpets have the shortest pile.