It is wise before you buy a carpet to check the density of the knotting by you self, because on this issue many salesman exaggerate a little.
It is something very simple, count the knots in length 1cm and in width 1cm and then multiply these two numbers, you now have the knots per square cm.
If you multiply x 10.000 you found the number of knots per square meter.
See the two examples below
each dot represents a knot.
Knotting calculation of carpets with even weave,
each pair of dots represents a knot.
For very accurate results must be measured at various points of the carpet and take an average,
or even better to count the knots in a bigger area eg 10x10cm and then multiply by 100.
Do not forget that the density is not the only criterion of the quality of a carpet but useful for comparing two similar carpets.
The number of knots , the knot type , material , origin , number and quality of colors even the design determine together the quality and price of a carpet.