Yarns are bought and sold by the pound or by the kilo, not by length. Sizes (or numbers) are used to express a relationship between unit length and weight of yarn.
There are two main numbering systems: direct numbering for filament yarns, and indirect numbering for spun yarns. Yarn size reflects the relationship between weight and length as well as the diameter of the yarn.
Direct Numbering
In the direct system as the numerical value of the size goes up, the weight per length and the diameter of the yarn increase accordingly. Direct numbered yarns are expressed in terms of weight in grams over length in meters. The most common direct numbering terms are as follows:
- Denier = Grams / 9000 Meters
- Decitex = Grams / 10,000 Meters
- Tex = Grams / 1000 Meters
The yarn number describes the total Denier and the number of the filaments in a bundle. For example, the number 150/48 means that the weight divided by 9000 meters is 150 and there are 48 filaments in the bundle.
Indirect Numbering
The indirect system reverses the relationship, the bigger the number the finer the yarn. The most frequently used numbers for indirect sizes are the Cotton Count (cc) and the Worsted Count (wc). Both of these numbering systems give the length of yarn per unit weight based on a hank.
Cotton Count
The cotton count expresses the number of hanks required to equal one pound of yarn. A hank of cotton is equal to 840 yards. Therefore, one cc is equal to 840 yards of cotton.
Two numbers that are separated by a slash such as 4/2 cc designate plied yarns. This equals 3360 yards (4 x 840) of two-ply yarn. This yields 1680 yards of yarn per pound (3360/2). A 8/4 cc yarns would yield the same number of yards per pound, but would be a 4 plies of finer yarn. So, a Number 8 four ply yarn is the same diameter as a Number 4 two ply yarn.
Worsted Count
The worsted count also expresses the number of hanks required to make a pound of yarn. A hank of worsted wool is equal to 560 yards. Therefore, one wc is equal to 560 yards of wool. Worsted sizes are expressed the reverse of cotton sizes. A two-ply number 6 worsted yarn would be expressed as 2/6 wc and would yield 1680 yards per pound.
You can convert worsted count to cotton count by multiplying the cc by 1.5.
