TPI stands for Twists Per Inch, which measures how tightly a yarn is spun. Higher TPI creates a firmer, more durable yarn. Lower TPI creates a loftier, softer yarn. To measure TPI, straighten a length of yarn without stretching it, mark one inch, and count the twists. For plied yarn, count the plying twists.

What are S-twist and Z-twist?

S-twist and Z-twist describe the direction of the twist. Hold the yarn vertically: if the twist spirals like the middle of the letter S (counterclockwise), it is S-twist. If it spirals like the middle of the letter Z (clockwise), it is Z-twist. Most commercially spun singles are Z-twist, and most plied yarns are S-twist (plied in the opposite direction to the singles).

How does twist affect knitting?

Higher twist yarns produce crisper stitch definition and more durable fabric, making them good for cables and textured patterns. Lower twist yarns are softer and loftier but pill more easily. Very high twist (crepe) yarns can cause fabric to bias (slant) in stockinette stitch. Balanced plied yarns minimise biasing.

KnitCalcs

Yarn Twist Calculator — TPI, Twist Angle & Classification

Calculate twists per inch, twist angle, and yarn twist classification for plied and singles yarns.

Twists Per cm

Count twists in 1cm of yarn

Yarn Diameter

Measure with a ruler

Number of Plies

Number of singles twisted together (e.g. 2 for a 2-ply)

Twist DirectionS = counterclockwise spiral, Z = clockwise spiral

How We Calculate This

This calculator converts twists per centimetre to twists per inch (TPI) and calculates the twist angle based on yarn diameter.

The formulas

TPI = Twists per cm x 2.54 (1 inch = 2.54 cm)

Twist angle = arctan(π x diameter x twist)

Diameter and twist must use matching units. This calculator works in metric throughout: diameter in centimetres (mm ÷ 10) multiplied by twists per centimetre.

The twist angle indicates how steeply the surface helix spirals relative to the yarn axis: a larger angle means a firmer, more tightly twisted yarn, while a smaller angle means a softer, loftier yarn. Because the angle depends on both yarn diameter and twist level, the "ideal" figure scales with the yarn's thickness rather than being a single fixed target.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard yarn weights and gauge. Results may vary with individual tension, yarn brand, and needle size.