Yarn fineness is an indicator used to measure the thickness of yarn. There are two commonly used calculation formulas in textile science: the fixed length calculation formula and the fixed weight calculation formula.

Fixed weight calculation formula:

1. English count (Ne) - a multiple of 840 yards of 1 pound weight yarn length under a common moisture regain, which means that 1 pound weight yarn is exactly 840 yards long, making it 1 count. The length of 1 pound weight yarn is 21 x 840 yards long, and the fineness of the yarn is 21 counts, written as 21 seconds. The imperial count is a fixed weight system, so the larger the count, the finer the yarn. The British count is not the legal yarn fineness indicator in China today, but it is still widely used in enterprises, especially in the cotton textile industry.

2. Metric Yarn Count (Nm) - The multiple of one gram of yarn length in meters at a common moisture regain, which means that one gram of yarn is exactly one meter long, making it one (metric) yarn count. One gram of yarn is 200 meters long, and the fineness of the yarn is 200 counts. The metric count is also a fixed weight system, so the larger the count, the finer the yarn. Both cotton and wool textile industries use it.