Four balls of cotton crochet thread, in red, yellow, orange, and silver.

A Guide to Crochet Thread Weights

What Is crochet thread?

Crochet thread is a popular alternative to regular yarn that is used to create lace, doilies, very lightweight accessories, baby clothes, jewelry, and other decorative items. 

What is crochet thread made of?

Crochet thread is sometimes referred to as “crochet cotton” since it is usually made from 100% mercerized cotton. “Mercerization” is a chemical process (using sodium hydroxide) that changes the nature of the cotton fibers. Mercerized cotton has more strength and shine than untreated cotton. It also has a much smoother feel. 

Other fiber content is less common, but you can also find crochet thread made of rayon, acrylic, silk, polyester, or some kind of blend.

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What are the different sizes of crochet thread?

The most important thing to know about the numbers assigned to crochet thread is that they are the opposite of the yarn weight numbering system: for crochet thread, the higher the number, the thinner the thread.

Crochet thread comes in sizes 3, 5, 10, 20, and 30, and is sometimes available in increments up to size 100. Size 3 is similar in thickness to Fingering Weight yarn and is often used to make garments; thread above size 10 gets progressively thinner and becomes more similar to sewing thread.

What size crochet hook is used for crochet thread?

Typically, crocheters use steel crochet hooks instead of regular hooks when working with very fine thread. Steel hooks tend to have much smaller heads and to be much stronger than regular hooks. Steel hooks come in sizes from 0.60 mm to 2.0 mm.

Common crochet thread sizes with recommended crochet hook sizes

  • #3 Crochet Thread (the thickest crochet thread; similar to yarn size #2, Fine);  recommended hook size: 3.5 – 3.75 mm
  • #5 Crochet Thread (similar to yarn size #1, Super Fine); recommended hook size: 1.75 – 2 mm
  • # 10 Crochet Thread (sometimes called bedspread weight; similar to yarn size #0, lace Weight); recommended hook size: 1.5 – 1.75 mm
  • #20 Crochet Thread; recommended hook size: 1.15 – 1.25 mm
  • # 30 and # 40 Crochet Thread; recommended hook size: 1 mm
  • # 60 and # 80 Crochet Thread; recommended hook size: 0.75 mm
  • # 100 Crochet Thread ; recommended hook size: 0.60 mm

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More Resources for Learning About Crochet Thread

How to Crochet With Thread For Beginners

CYC Yarn Weight System

Cotton Crochet Thread Sizes and Equivalents

A Beginner’s Guide to Crochet Thread

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