Thread count or Threads Per Inch

Thread count or threads per inch (TPI) is a measure of the coarseness or fineness of fabric. It is measured by counting the number of threads contained in one square inch of fabric including both the length (warp) and width (weft) threads.

The fabric thread count is the number of threads counted along two sides (up and across) of the square inch, added together. An example is that if 100 lengthwise threads are woven with 100 widthwise threads that would produce a thread count of 200.

Thread count is often used as a measure of fabric quality, so that "standard" cotton thread counts are around 150 while good-quality sheets start at 180 and a count of 200 or higher is considered percale. Some, but not all, of the extremely high thread counts (typically over 500) tend to be misleading as they usually count the individual threads in "plied" yarns (a yarn that is made by twisting together multiple finer threads). For marketing purposes, a fabric with 250 two-ply yarns in both the vertical and horizontal direction could have the component threads counted to a 1000 thread count although "according to the National Textile Association (NTA), which cites the international standards group ASTM, accepted industry practice is to count each thread as one, even threads spun as two- or three-ply yarn. The Federal Trade Commission in an August 2005 letter to NTA agreed that consumers 'could be deceived or misled' by inflated thread counts. In 2002, ASTM proposed a definition for "thread count" that has been called "the industry's first formal definition for thread count".  A minority on the ASTM committee argued for the higher yarn count number obtained by counting each single yarn in a plied yarn and cited as authority the provision relating to woven fabric in the Harmonized Tariff Schedule of the United States, which states each ply should be counted as one using the "average yarn number."

Standard Test Method for Warp (End) and Filling (Pick) Count of Woven fabrics This test method covers the measurement of warp end count and filling pick count and is applicable to all types of woven fabrics.

Thread count terminology is often used especially in regard to cotton linens such as bed sheets, and has been known to be used in the classification of towels. It is also used to describe dress shirt fabrics and other fabrics.