Yarn Weight in Tex, Denier and WPI

Yarn weight describes the thickness (linear density) of yarn.

Key relationships:

• Tex = grams per 1,000 meters of yarn
• Denier = grams per 9,000 meters of yarn
• 1 tex = 9 denier (exact)
• 1 denier = 0.1111 tex

WPI (Wraps Per Inch): WPI measures how many times yarn wraps around a ruler per inch. Thicker yarn = fewer wraps. Thinner yarn = more wraps.

Standard yarn weight categories (approximate): WPI below follows the eight-band Craft Yarn Council scale, the same one the yarn weight converter with needle and hook sizes uses, so the two pages agree. Be aware that finer-grained charts exist which split lace into cobweb, lace and light fingering, and those quote 30 to 40 wraps for true lace rather than the open-ended “18 or more” here. Neither is wrong; they are cutting the same range into a different number of bands.

WPI is an approximation since it depends on fiber type and twist.

Tex and denier both measure linear density, the weight of a fixed length of yarn, just on different reference lengths. Denier (grams per 9,000 m) comes from the silk trade and survives in synthetics, which is why pantyhose are sold as “20 denier” or “70 denier,” the higher number being thicker and more opaque. Tex (grams per 1,000 m) is the cleaner, more modern unit, and the two convert simply since one tex is nine denier.

WPI, or wraps per inch, is the hand-knitter’s practical trick: wind the yarn around a ruler and count the wraps in an inch. It needs no scale and works with a ball that’s lost its label, which is why crafters rely on it. The catch is that the standard weight categories (lace, fingering, DK, worsted, bulky) overlap at the edges and depend on fiber and twist, so two “worsted” yarns can knit up noticeably differently. Always check gauge with a swatch rather than trusting the category alone.

Needle and hook sizes by category

These are starting points printed on the ball band, not rules. The needle you actually want is whichever one hits the gauge your pattern asks for, and it is normal to go a size either way. Knitters who purl tightly often need to go up one; loose knitters go down.

How to measure WPI properly

Wrap the yarn around a pencil or ruler for an inch, laying the wraps side by side without stretching and without squashing them together. Count the wraps. The two mistakes that throw the number off are pulling the yarn tight, which thins it and inflates the count, and letting the wraps overlap.

Do it three times in different places along the yarn and take the middle value. Single-ply and loosely spun yarns compress much more than a firm 4-ply, so the same tex can wrap quite differently. That is the honest limit of the method, and it is why the table above gives ranges rather than points.