The twist number is the number of times that a yarn is twisted around its axis before it is unwounded. It is preferably reported in twist per meter (TPM).

To measure the twist count, the twist direction is to be determined under Iranian National Standard No. 11261 or ISO 2:1973 (either an S-twist or a Z-twist). The yarn of a certain length is then placed between the fixtures of the test machine, and a certain tensile force (0.05 cN/dtex) is applied using the weight set.

Then, the other parameters, including the twist direction, rotational speed of the fixture, yarn length, and yarn denier, are introduced to the test machine before the test is initiated.

Several tests are conducted to ensure the reliability and validity of results.

The outputs include TPM, average twist, twist factor, and variation coefficient.