Tex
Also searched as: tex system, decitex, dtex, kilotex, ktex, millitex, linear density, grams per kilometre, grams per kilometer
Tex is the direct, metric unit of linear density for fibers and yarns: the mass in grams of 1,000 meters of material, with decitex (dtex) giving grams per 10,000 meters.
In detail
Tex belongs to a direct numbering system, so a larger number means a heavier, coarser strand for the same length. The same unit is intended for every stage and fiber type, from single fibers through slivers, rovings, tops, singles and plied yarns, cords and threads. Decimal prefixes keep the numbers convenient: decitex is common for filaments and staple fibers, while kilotex suits heavy slivers. Because tex, decitex and denier are all mass per length, they convert by fixed factors and never require knowledge of the fiber's density or cross-section.
The science and numbers
Linear density in tex is mass divided by length, expressed as grams per kilometer. Useful identities follow directly from the unit definitions: 1 tex equals 10 dtex, 1,000 millitex and 9 denier, so dtex is about 1.11 times the denier value. Tex converts to indirect counts by division: English cotton count Ne is about 590.5 divided by tex, and metric count Nm is 1,000 divided by tex. ASTM D861 sets out practice for designating linear density in tex, and ISO 1144 specifies the universal Tex System with recommended multiples and submultiples. Conversion tables replacing traditional counts with rounded tex values appear in ISO 2947 and ASTM D2260. In laboratory work, yarn linear density is found by weighing measured skeins after conditioning, since moisture content changes mass.
A practical example
A mill lists a polyester staple as 1.7 dtex and a finished yarn as 20 tex. The fiber figure describes individual fibers; the yarn figure describes the whole twisted strand. Converting, 1.7 dtex is about 1.5 denier, and 20 tex equals 200 dtex or 180 denier. Keeping track of which object each number describes prevents a buyer from comparing a fiber specification with a yarn specification.
What to distinguish
Tex is not diameter. Two yarns of equal tex can differ in thickness because polymer density, fiber packing, twist and bulking all change how much space a given mass occupies. A plied yarn's resultant tex also differs slightly from the simple sum of its singles because twisting shortens the components. Always check whether a figure refers to a fiber, a singles yarn or a finished plied yarn.
Origins and history
Before tex, each branch of the trade used its own count: cotton hanks, worsted hanks, woollen runs, linen leas and silk or filament deniers. ISO Technical Committee 38 on Textiles worked on a single metric replacement in the 1950s, and A. G. Scroggie described the Tex universal yarn numbering system in Textile Research Journal in 1958. ISO later published the system as ISO 1144, with a 1973 edition and a current 2016 edition, alongside the ISO 2947 integrated conversion table of 1973.
Related terms
Sources & further reading
- ISO: ISO 1144:2016 Universal system for designating linear density (Tex System)
- ASTM: D861 Standard Practice for Use of the Tex System to Designate Linear Density
- Textile Research Journal: The Tex Universal Yarn Numbering System (Scroggie, 1958)
- ISO: ISO 2947:1973 Integrated conversion table for replacing traditional yarn numbers by rounded values in the Tex System
Technical references reviewed 2026-09-22. Examples are illustrative. Industry organizations and manufacturers describe their own fields; their references are not independent product endorsements. Figures are approximate and depend on the stated test conditions.