The Rug Library

Higher knot density generally allows finer design detail but also means longer weaving time and higher cost.

Knot density is usually expressed as knots per square inch (KPSI), found by multiplying the number of knots counted along one inch horizontally by the number along one inch vertically.

Knot density in handmade pile carpets varies enormously, from around 25 to 1,000 or more knots per square inch, and is a traditional but not sole indicator of quality.

Knot counts are not comparable across all rug types: a coarse tribal rug and a fine city carpet can each be well made, as density depends on style, origin and materials.

Knot density is also expressed per square centimetre or per square decimetre, units common in European and Iranian references.

A rug counted at 10 knots per inch horizontally and 10 per inch vertically has a density of 100 knots per square inch.

Dealers commonly describe rugs under about 80 knots per square inch as coarse, around 100 as medium and around 200 or more as fine, though these bands are informal.

Because asymmetric knots can be packed more tightly than symmetric ones, very high knot densities are usually associated with asymmetric knotting.

Kashmiri workshop tradition equates more knots with a finer carpet, and silk carpets there are known for especially fine knotting.