Worked example: counting and converting
On the back of a rug, an inspector lays a ruler along the weft and counts 10 knots in one inch, then along the warp and counts 12 knots in one inch.
- KPSI: 10 × 12 = 120 knots per square inch.
- Per square metre: one square metre is about 1,550 square inches, so 120 KPSI is about 186,000 knots per square metre.
- Repeat: the count is taken at three or more places away from the edges, because a weaver's tension can drift across a large rug.
If the purchase order says 120 KPSI and the counts read 120, 118 and 96, the low reading is the finding, not the average.
What KPSI does not tell you
Knot density says nothing about wool quality, dye quality, washing or finishing. A dense rug in poor wool can wear worse than a coarser rug in good wool. KPSI also applies only to knotted pile. Hand-tufted, hand-loomed and flatwoven rugs have no knots to count, so their specification uses pile weight, pile height or picks per inch instead. Mills often quote quality in their own codes, so put the KPSI figure, or a knots-per-square-metre figure, in the order rather than a code.
How Clear To Load checks KPSI
On a hand-knotted rug inspection our inspector counts horizontally and vertically on the back at three or more places, photographs the counts, and reports in the unit your purchase order uses. A count below the agreed figure, or a much lower count in one part of the rug, is reported as a defect. The count is usually checked alongside abrash, size and diagonals. Hand-knotted rugs for export are woven in clusters such as Bhadohi-Mirzapur and Srinagar.