In the Varanasi area of India, rugs are graded using two numbers, like "5/40," "9/60," or "12/60." The first number represents the knots in 9/10 of an inch of the rug's width. The second number represents the knots in 4 1/2 inches of the rug's length. 0.9" x 4.5" equals 4.05", almost four square inches, so an easy conversion is to multiply the two numbers together and divide by 4 (sq. in.) to get the approximate weave in knots per sq. in. For example, with a "9/60" quality rug, 9 X 60=540 and 540/4=135 knots per sq. in. Note that most rugs from India have strongly offset warps, so you will only see one element of the knot on the back of the rug.

In Pakistan, indicated qualities like "16/16" or "16/18" for rugs in Persian design represent the number of knots per linear inch across the warp and weft counted in the normal way. For example, a "16/18" quality Kashan has 16 X 18 weave, or about 288 knots per sq. in. Note that these rugs have strongly offset warps, so you will only see one element of the knot on the back of the rug.

So-called "double" Bokharas from Pakistan in qualities like "9/18," "10/20," "11/22," and "12/24" are different. In this type of rug, warps lie side-by-side and are not offset, so both elements of the knot show on the back of the rug. Be sure not to double-count the weave across the width when examining a Bokhara.

China uses a completely different nomenclature, with "line counts" like "70 line," "90 line," or "120 line." The line count equals the number of knots in a linear foot measured across the width of the rug. Thus a "90 line" rug has 90 knots per linear foot across its width. A "90 line" Chinese rug has about 56 knots per sq. in.; a "SINO-PERSIAN" (a Chinese rug in Persian design) in "160 line" quality has about 177 knots per sq. in.; a "240 line" rug has about 400 knots per sq. in. Chinese rugs have strongly offset warps, so you will only see one element of the knot on the back of the rug.