The yarn count refers to the thickness of yarn, usually can be expressed as S, D, N, Tex, Dtex etc.
S is an English yarn count, which refers to a weight of a pound of yarn at a fixed return rate. Generally, the yarn count of short fiber is denoted as S, the English of short fiber can be expressed as Spun. The thicker the yarn, the smaller the S; the finer the yarn the higher the S; for example, 20S is thicker than 40S.
D is the abbreviation of Denier (Daniel), a fineness representation of chemical fibers, which refers to the number of grams of weight of 9000 meters long silk at the rate of moisture regain. The yarn count of long fiber is expressed as D, and the long fiber is expressed in English as Filament. The bigger the D, the thicker the yarn; for example, 75D is thicker than 50D.
Tex is also known as the "number". It refers to the number of grams of 1000 meter long yarn weight at the fixed moisture return rate.
Nm refers to the multiple times of the length of 1 grams of heavy yarn, which means that the weight of the 1 gram heavy yarn is 1 meters. The length of the 1 gram weight yarn is 200 meters, and the fineness of the yarn is 200NM. The metric is also a fixed weight system, so the larger the NM, the thinner the yarn.
Dtex refers to the number of grams of fiber bundles 10000 meters long.