Knot Count (KPSI) Explained in Oriental Rugs

What Is KPSI? Understanding Knot Count in Oriental Rugs

KPSI, or Knots Per Square Inch, is a commonly cited measurement used to describe the knot density of a hand-knotted rug. It is calculated by counting the individual knots along one inch vertically and one inch horizontally on the reverse of the rug, then multiplying those two numbers together.

While KPSI can offer insight into a rug’s fineness and weaving effort, it is only one of many factors considered by rug experts when evaluating quality, value, and craftsmanship.

KPSI is sometimes referred to as knot count or knot density, though these simplified terms can obscure a more complex reality: knot density is not measured uniformly across all regions, traditions, or weaving systems.

What Is KPSI?

KPSI measures how many individual knots appear within a one-square-inch area of a hand-knotted rug. Because knots form the structural and visual foundation of a rug, higher knot density often allows for more detailed designs and finer articulation.

However, KPSI alone does not determine quality, value, or desirability.

How Is KPSI Measured?

KPSI is measured on the back of the rug, not the front.

1. Count the number of knots in one inch horizontally
2. Count the number of knots in one inch vertically
3. Multiply the two numbers together

Example: 10 knots across × 10 knots down = 100 KPSI

This method provides a standardized reference point—but only when counted correctly. In an ideal sampling, the measurement would be an average of 3 separate areas in some distance from one another, away from the edge of the carpet which may often be unusually finer or more coarse.

How Important Is KPSI?

KPSI should always be considered in context.

Knot density can vary significantly depending on:

• Region of origin
• Weaving tradition
• Intended function of the rug
• Time period and workshop
• Knot type and loom orientation

A high knot count does not automatically mean a rug is superior, just as a lower knot count does not imply poor quality. Many highly respected rugs—particularly tribal or village weavings—were never intended to be densely knotted.

Is Knot Count as Simple as It Sounds?

Not at all.

One of the most common counting errors is mistaking double-ply yarn for two separate knots. This mistake can dramatically inflate perceived KPSI. Similarly, two nodes of one knot on the horizontal may appear to be separate, but may easily be misconstrued and inflate density.

Example:

• A rug correctly measuring 10 × 10 knots (100 KPSI)
• May be miscounted as 10 × 20 knots (200 KPSI) if yarn ply is misunderstood

Other common sources of error include:

• Misidentifying knot types
• Offset or staggered loom construction
• Counting decorative elements rather than structural knots

In some cases, inflated knot counts may stem from misunderstanding. In others, they may be used deliberately to misrepresent quality.

Why KPSI Varies by Region

Not all rug-producing regions historically used KPSI as their primary measurement system.

Examples include:

• Tabriz, Iran, where quality is traditionally measured using the raj system
• Chinese rugs, which use line as a density metric

While these systems can be loosely translated into KPSI, they are not equivalent and should not be treated as such. Two rugs with the same translated KPSI may differ substantially in appearance, structure, and intent.

What Is a “Good” KPSI?

There is no universal benchmark for a “good” knot count.

Context matters.

• A 250 KPSI ca. 2000's Peshawar rug would be unusually fine for that category
• A 250 KPSI ca. 1970's Nain rug would be considered very low within its own tradition
• A 250 KPSI ca. 1890's Silk Heriz rug is not uncommon.
• And to add more dynamic... A 250 KPSI ca. 1890's Wool Heriz rug would be nearly unheard of as they often average 70 - 120 KPSI yet remain highly coveted and sought after at that....

Knot-for-knot comparisons across different rug types are rarely meaningful. There is no fixed dollar value per knot, and no ideal KPSI that applies across all Oriental rugs.

Typical KPSI Ranges in Oriental Rugs

Knot density in hand-knotted rugs can range widely, from as low as 15 KPSI to well over 2,500 KPSI.

• KPSI above 800 is extremely rare or virtually non-existent for rugs pre 1920. However, it may be considered uncommon post 1920.
• Exceptionally fine examples may exceed 1,400–2,500 KPSI.
• Ultra-fine workshop rugs, such as Kum Kapi or certain Indian and Persian silk pieces, represent the extreme upper end

These rugs are rare and labor-intensive, but still must be evaluated holistically rather than numerically.

Seeing Knot Count in Practice

Understanding KPSI conceptually is helpful, but seeing knots counted on the back of a rug provides clearer context. In the video below, knot density is examined directly, including common counting errors and why inflated knot counts are easy to misinterpret.

This visual reference reinforces why KPSI should always be evaluated alongside structure, materials, and weaving tradition.

Here's a chart showing comparative knot density qualities in the industry, and reference according to popular weaving areas. KPSI is the US measure, RAJ Persian, Line Chinese, there are several varieties in India, and Pakistan as well.

Final Takeaway

KPSI is a useful reference, not a verdict.

True evaluation of an Oriental rug considers:

• Materials
• Design integrity
• Weaving tradition
• Condition
• Age
• Aesthetic and cultural significance

Knot count is only one thread in a much larger fabric.