Yarns are bought and sold by the weight, not by length. Because of this sizes (or numbers) are used to express a relationship between unit length and weight of yarn. In this section you will learn about the two numbering systems and how those systems relate weight length and size of the yarn.
There are two main numbering systems- direct numbering for filament yarns and indirect numbering for spun yarns. While yarns sizes reflect a relationship between weight and length, this relationship also reflects the diameter or thickness of the yarn, although not as precisely. Basically the relationship to size is expressed in that a low weight yarn is finer (smaller) than a high weight yarn of the same length. This relationship becomes less precise due to variations is twist and fibers. Therefore sizes express the relationship between weight and length in a yarn and a close, but not precise, relationship to diameter.

Direct Numbering
In the direct system as the numerical value of the size goes up, so does the weight per length and the diameter increase correspondingly. Direct numbering are expressed in terms of weight in grams over length in meters. The most common direct numbering terms are:

	Denier- Grams/9000 M
	Decitex- Grams/ 10,000 M
	Tex- Grams/1000

The yarn number describes the total Denier and the number of 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 (Ne), Numeric Count (Nm) and the Worsted Count (wc). Both of these numberings give the length of yarn per unit weight based on a hank.

Cotton Count (NE) The cotton count expresses the number of hanks required to make a pound of yarn. A hank of cotton is equal to 840 yards. So 1 cc= 840 yards of cotton, the coarsest cotton yarn. A 3 cc yarn would then be one third as course and would be expressed as 3/1 cc show that it is a single strand.
Likewise plies are designated by two numbers separated by a slash such as 4/2 cc. This equals 3360 yards (4 x 840) of two ply yarn. This yields 1680 yards of yarn per pound (3360/2).
An 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.

Numeric Count (NM)

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. So 1 wc= 560 yards of cotton, the coarsest worsted yarn. 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 covert worsted count to cotton count by multiplying the cc by 1.5, or wc= cc x 1.5.