Persian & Oriental Knots - How Are Knot Counts Measured?
Persian rugs > Persian Rug Guides > Persian & Oriental Knots - How Are Knot Counts Measured?
There are various measurements involved in the different areas when establishing how fine a rug is woven. The main measurement is KPSI (knots per square inch), similar to the pixels on a TV or computer screen the more pixel (or knots) the clearer and sharper the image. This is typically measured by counting the knots on the back of a rug across a vertical and horizontal inch and multiplying the two numbers. A 12x12 rug would have 144 KPSI.
A square inch measurement of a fine rug around 20/20 or 20/21 (~ 400KPSI).
Note that the knotting in some rugs makes them look like they have twice as many knots horizontally than they actually have. The red circles show 2 nodes, this is actually only one knot. You will notice there is no colour on this rug which appears to have only a single node in the way the one above it has.
There are however slightly different measurements used in certain areas, this guide will explain these and show you how these translate into KPSI:
In certain areas of India, such as Bhadohi, Oriental rugs are measured using two numbers, for example: "5/40", "9/60" or "13/65". These numbers are called the bis and bhutan. The first number, or bis, is the number of knots in 9/10ths of an inch across the horizontal plane - so 9 would be 10 knots across (9/0.9=10). The second number, or bhutan, is the number of knots vertically in 4 1/2 inches. Therefore 60 bhutan is the equivalent of around 13 knots per vertical inch. A "9/60" rug would therefore be around 130 KPSI (10x13=130).
A quick method of calculating the Indian measurement is to multiply the two numbers and divide them by 4.05 (9x60=540... 540/4.05=133).
Chinese rugs use a measurement called line counts. This is typically described as "90 line" or "120 line" and refers to the number of knots (actually pairs of warps) measured in a linear foot of rug. In Chinese rug construction the number of knots vertically and horizontally are normally the same so a 120 line carpet has 100 KPSI (120/12=10... 10x10=100).
Rugs from Pakistan are normally described by the actual number of knots vertically and horzintally e.g. "16/16" or "16/18" which would equal 288 KSPI (16 x 18). These are called "double knot" which seems counter-logical. In Pakistan and in other countries you also get a "single knot" rug (such as in the 2nd picture above), to the unaware these seem to have a lot more knots in them than they actually have. The shape of the knots makes it look like there are two knots rather than one, you will notice on these rugs that there is never a colour (such as at the peak of a flower or triangle shape) which has what looks to be only one knot. There will always be two. These are measured in much the same way e.g. 9/16 which is 144 KPSI.
Even the Persian rugs have different measurements to denote the fineness of a carpet:
In Tabriz the term Raj is often used rather than KPSI - this is the number of knots across 2 3/4 inches of a rug. Typical measurements are "30 raj", "35 raj", "40 raj" or the super fine "60 raj". A standard quality Tabriz at 35 raj would translate to around 162 KPSI (35/2.75=12.73... 12.73x12.73=162).
Nain rugs use the term LAA, this does not directly translate to KPSI but is the number of yarn threads in an individual fringe at the end of a rug. The lower the LAA the higher quality the rug. Having a lower LAA means there can be more warp strings across the width of the carpet as each strand is finer which in turn allows more knots to be tied in a given area - since knots are tied around the warp string (which show as fringes at the top and bottom of a rug) then logic determines that the more warps in a rug mean equals more knots. To measure a fringe strand is unravelled which may contain 3 thin threads, one of these is unravelled again which could have another 3 threads (3x3) making it a 9 LAA rug called a Nola (nahola) in Farsi. A 6 LAA rug (3x2) is called a Shisla (shishla) and the finest rugs at 4 LAA (2x2) are Charla (sharla).
Isfahan rugs sometimes have different coloured threads between the fringe and the rug's pile called kheft, this is measured across one metre and the number of different threads is an indication of quality.