There are 3 yarn count systems in common use today. They are:
1. The Fixed Weight System (FWS)
2. The Fixed Length System (FLS)
3. The Tex System (Tex)

The Fixed Weight System is based on the length of spun yarn obtained from 1 pound of fibers. The longer the length of the spun yarn, is, the finer the yarn, and the higher the count number. The shorter the yarn, the thicker it is and the lower the count number.
This is the system that is used to figure the count of yarns spun from wool, cotton, linen, and silk.

The Fixed Length System is used for continuous filament (extruded) yarns and reeled silks. It is based on a fixed length of yarn with the weight of that length of yarn being variable. The Fixed Length is 9,000 meters and the weight is stated in grams. The higher the denier number is, the coarser the yarn. As an example, 9,000 meters of reeled silk weighing 20 grams would have a denier count of 20; while 9,000 meters weighing 40 grams would have a denier of 40 and would be the coarser of the two yarns.

The Tex system of yarn count came into being in 1962 when the International Organization for Standardization saw that globalization of trade required a world-wide standard for measuring yarns. Up until this time yarn measurements varied considerably by the physical location of spinning mills. Tex is a fixed length system with the count in grams per kilometer (1000 meters) of yarn. A yarn marked as being “20 Tex” would weigh 20 grams per kilometer. The Tex number increases as the thickness of the yarn increases. There is an international labeling code for yarns marked with Tex sizes. On this system, “folded” means plied, and twist direction is included with size labeling. So a Tex label would read: R 40 Tex/ 2 s. This label tells us that two threads of 20 Tex have been plied or folded together using S twist and that the Tex count of the resulting yarn is 40. (R = Resultant count)

As hand spinners, the Fixed Weight System is the one that we are most concerned with as this is the system that is used to figure the count of yarns spun from wool, cotton, linen, and silk.