Turns per Inch (TPI)

TPI means turns per inch. It tells you how many turns of twist a yarn has per inch of length. TPM measures the same quantity in turns per meter.

How It Works

One inch equals 25.4 millimeters. Multiply TPI by about 39.37 to get TPM. Specify the twist direction, S or Z, separately.

Uses and Benefits

Using the same twist unit makes supplier specifications easier to compare. In a staple-spun yarn, twist helps the fibers hold together.

Limitations

A coarse yarn and a fine yarn with the same TPI can have different fiber angles and feel different. Twist alone does not establish strength or yarn quality.

What to Check

Record the twist unit, direction, yarn count, and whether the yarn is single or plied. Make sure the test result refers to the twist you want to compare.