Yarn Count or Yarn Number

Yarn Count:

The count of Yarn is a numerical expression, which defines its fineness. Spun Yarns are only roughly circular in cross-section and irregularity in thickness is unavoidable. Filaments Yarns with only a small amount of twist in them are referred to as a flat yarns with solid bodies.
A definition of Yarn Count is given by the Textile Institute  (UK) : Yarn Count is number indicating the weight per unit length or the length per unit weight of yarn. However, various counting systems using different units of weight and length are in use. 
We use mainly two counting system as :
1. Direct systems of Yarn Count.
2. Indirect systems of Yarn Count.

1. Direct system of Yarn Count :

In this system, Yarn Count is the weight of a unit length of Yarn. The units of weight and length vary from trade to trade, district to district and country to country. However, a general formula which applies to all directs systems can be written as follows:
Let N= the Yarn count,
W= the weight of the sample at the official regain in the units of the system.
L= the length of the sample,

Then, N= W×l/L

Math :  If a skein of 100 m of filament Viscose Yarn weight is 1.67 g, Calculate its Denier.

Solutions: In the Denier system the weight unit is the gram and the unit of length is 9000 m.

Thus, W=1.67g, L=100m, and l = 9000 m. 

We know, N= W×l/L, therefore,

Denier = N= W×l/L = 1.67×9000/100 = 150.3;

So the Yarn Count is 150.3 Denier.

2. Indirect System of Yarn Count

In this system Yarn Count is the number of units length per unit weight of Yarn. Here again there are various units of length and weight and numerous systems. However, a general formula which applies to all indirect systems can be written as follows:

Let, N= The Yarn Count,

W= The weight of the sample at the official regain in the units of the system, w= the unit weight of the system, L= the length of the system, and l= the unit length of the system,

Then N= L×w/l×W