Crochet Thread Sizes Explained

The numbering, and why it is backwards

Thread numbering descends from cotton count, an old textile system where the number describes how many lengths of a given weight you get from the fiber. More lengths per unit weight means a finer thread - so a larger number means a thinner thread.

You do not need the history to use it. You need one rule: higher number, finer thread. The manufacturer of the most widely sold range states it plainly of its own size 3 line, describing it as thicker than, and working up faster than, its smaller-numbered threads.

The sizes in common production

Sizes 40, 50, 80 and above exist in specialist tatting and bobbin lace threads. They are not what a crochet pattern means, and they are not generally stocked alongside yarn.

Where thread sits against yarn

Crochet thread is not a separate universe from yarn - it is the bottom of the same scale. The Craft Yarn Council's category 0 covers both lace weight yarn and 10-count thread.

That is one row, for one thread size. The standard does not define rows for sizes 3, 20 or 30 - which is exactly why patterns in those sizes name a specific hook rather than a category. The full weight table is on the yarn weight chart.

Steel hooks, and the brand problem

Steel hooks are numbered on their own scale, which also runs backwards - a steel 14 is finer than a steel 0. That much is consistent.

What is not consistent is what those numbers mean in millimeters. Two ranges we list both make a hook called No. 10, and they are not the same tool.

A 0.4mm difference sounds small and is not - it is more than a third of the smaller hook's diameter. Always work from the millimeter size, never from the steel hook number. This is the single most useful thing on this page, and hook size chart covers the regular-hook scale alongside it.

Which thread size for which project

• Doilies, coasters and traditional lace: size 10. Almost every vintage pattern in circulation assumes it.
• Tablecloths and bedspreads: size 10 for a normal lifetime, size 20 or 30 if you want the fineness and have the patience.
• Shawls and wearables: size 3, which drapes and works up faster.
• Amigurumi in miniature: size 10, worked tightly.
• Jewelry, snowflakes, edgings: size 20 or finer, where the stiffness after starching matters more than the speed.
• Your first thread project: size 3. Everything is the same, at a scale you can see.

Gauge in thread

1. Swatch, as with yarn. Thread gauge varies at least as much between crocheters as yarn gauge does.
2. Measure over more stitches. At 32 to 42 double crochet per 4in, a one-stitch error over four inches is a much larger proportional error than in worsted.
3. Expect to go down a hook size from whatever the pattern says if your tension is loose - thread shows loose tension far more visibly than yarn does.
4. Block before measuring. Thread lace opens up dramatically when blocked, and an unblocked swatch is not the fabric.

Knitting gauge and swatching covers the method; it applies unchanged to crochet, only the stitch names differ.

Mercerization

Almost all crochet thread is mercerized cotton. Mercerization treats the cotton under tension in a caustic solution, which makes the fiber smoother, stronger and more lustrous, and helps it take dye.

For thread crochet that matters three ways: the sheen is a large part of why a doily looks the way it does, the added strength survives being worked at very tight tension, and the smooth surface means the hook does not fuzz the thread as it works. Cotton yarn pros and cons has the fiber side.

Buying by yardage

Thread is sold in balls whose yardage varies by color within the same product - one common size 10 line gives 400 yards in white, ecru and natural, 350 in solid colors and 300 in shaded colors.

That is a 25 percent swing across one product, so a pattern quoting 'two balls' is quoting two balls of one particular color family. Convert to yardage before you buy, as you would for any yarn - how much yarn do I need has the arithmetic, and the same area method works for a doily.