There are two main methods for expressing the fineness of yarn: fixed length and fixed weight. ‌

Fixed length system

Fixed length system refers to the weight of fibers or yarns of a certain length. The smaller the value, the finer the fiber or yarn. Common fixed length units include:

Tex: Refers to the weight of 1000 meters of yarn at a predetermined moisture regain. The smaller the weight, the finer the yarn. It is commonly used for woolen yarn.

Dtex: Refers to the weight of 10000 meters of fiber at a predetermined moisture regain. The smaller the dtex, the finer the fiber, commonly found in fiber yarns.

Denim (Nden): Refers to the weight of 9000 meters of fiber or yarn at a predetermined moisture regain. The smaller the denier, the finer the yarn. It is commonly used for natural fibers such as silk or synthetic fibers.

Fixed weight system

Fixed weight system refers to the length of fibers or yarns with a certain weight. The larger the value, the finer the fiber or yarn. Common fixed weight units include:

Metric count (Nm): Refers to the length of 1 gram of yarn at a nominal regain, with a larger count indicating finer yarn.

Imperial count (Ne): Refers to a multiple of 840 yards in length for a 1-pound yarn at a nominal regain, with a higher value indicating finer yarn.