Direct counting system
The direct method, called the fixed length, variable weight method, is given by the ratio of the weight divided by the length (T=W/L).
This method is commonly used for all yarns made with continuous fibres (silk, rayon, nylon etc.)

The Tex count (Tex) indicates the weight in grams of 1,000 metres of yarn.
For example, Tex 1 means that 1,000 metres weighs 1 gram.This counting method is called universal and ought to replace all other count systems, especially the indirect system (N).

The Decitex (Dtex) count indicates the weight in grams of 10,000 metres of yarn or filament
This method is used for filaments or multifilament yarns.
For example, Dtex 1 means that 10,000 metres weighs 1 gram (filament).

The Denier (Den) count indicates the weight in grams of 9,000 metres of yarn or filament.
It is used for filaments, for multifilament yarns and for silk.
For example, Den 1 means that 9,000 metres weighs 1 gram (filament).
With the direct method, the number indicating the count is higher the larger the yarn (or filament), the count being expressed as a function of the variable weight compared with a fixed length.