What is KPSI/WPF/KPSM?

WPF, warp per foot.

It shows how many warp we use before weaving a rug. When we produce a rug, we need to hang up warp line first, after all warp of a full rug width been set up, then the weavers start to knotting double knots on each warp line. The more warp a rug got, the more KPSI/KPSM it will got.

KPSI, knots per square inch.

It's a unit we show how many knots we can count from a Persian silk rug, in a size of one square inch. It is a density unit we mark grade of a rug, the more knots it has, the smaller knots it got, and it also means each pixes would be smaller, so the pattern will with more details. It's a main unit to show how good a rug is.

How to calculate WPSI?

1.By WPF parameter data.
For example, a rug that with 260 WPF(warp per feet), it has 260/12=22 warp or knots in a inch, so 22 by 22=484 knots per square inch.
2.By count from a rug.
With your eyes, camera or magnifier, with a ruler you can count how many knots in a inch, then we can calculation how many knots in one square inch. For example you count 22 knots in a inch, so it has 22 by 22=484 KPSI.

KPSM, knots per square meter.

It's a unit we know how many knots in an area of one square meter from a Persian silk rug.
It's unable to count knots one by one in a square meter size, so we always cacutate it from WPF or KPSI.

How to calculate WPSM?

For example, a rug with 260 WPF, or 484 KPSI
Calculate from 260 WPF: 1 meter has 100 cm, and 30.48cm is one foot. So it's 3.28 feet for 1 meter. Use 3.28 by 260=852 warp per meter, 852 by 852=725,904 knots per square meter.
Calculate from 484 KPSI: 1 square inch=2.54 by 2.54=6.4516 square cm, 1 square meter=100 by 100=10,000 square cm, so 1 square meter=10,000/6.4516=1550 square inch, 1550 by 484=750,200 knots per square meter.