Standard Active Last Updated: Jul 26, 2018
ASTM D861-07(2018)

Standard Practice for Use of the Tex System to Designate Linear Density of Fibers, Yarn Intermediates, and Yarns

Significance and Use

4.1 The tex system has been approved for general use by the International Organization for Standardization, Technical Committee 38 on Textiles (ISO/TC 38), which has also recommended a list of rounded tex numbers for use with fibers and all types of yarns. Conversion tables showing the rounded tex numbers corresponding to various numbers in different traditional systems are given in Tables D2260 and ISO 2947.

4.2 The tex system for designation of the linear density of fibers and yarns is a direct system based on mass per unit length, M/L, and employs metric units of length and mass. The tex unit, grams per kilometre (1000 m) has been approved by ISO/TC 38 for use with all fibers and all types of yarn. The committee has also approved the use of kilotex and decatex numbers for coarse structures and decitex and millitex numbers for fibers.

4.3 The tex system relates to the property commonly associated with coarseness, or inverse fineness of a yarn because the tex numbers increase with an increase in the size or mass per unit length of the yarn. The tex system is intended for use by all branches of the textile industry, in all countries, for yarns made from all types of fibers or mixtures of fibers.


1.1 This practice covers the use of the tex system to designate the linear density (number, or count) of fibers and of yarns made from any type of fiber or combination of fibers. It is also applicable to other textile materials, including yarn intermediates (slivers, rovings, tops, and so forth), single or plied yarns, cords, and threads.

Note 1: The mass per unit length concept of linear density is applicable to any material which has a high ratio of length to cross section.

1.2 Conversion factors for various indirect and direct yarn numbers to exact tex equivalents can be found in Standard Tables D2260.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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Book of Standards Volume: 07.01
Developed by Subcommittee: D13.58
Pages: 2
DOI: 10.1520/D0861-07R18
ICS Code: 59.080.20