The Ultimate Guide to Crochet Thread Sizes (And How to Choose the Right Hook)

If you have spent any time in the yarn section, you already know the unwritten rule of standard yarn: the bigger the number, the thicker the yarn.

When you make the leap to crochet thread, however, that logic completely flips upside down. Suddenly, a Size 3 thread feels like a thick, cozy cord, while a Size 100 looks like spider-web silk.

Whether you are aiming to make delicate lace doilies, vintage tablecloths, lightweight summer jewelry, or micro-crochet amigurumi, navigating the world of crochet thread can feel intimidating. This guide breaks down how thread sizing works, how to choose the right hook, and which projects work best for every thread weight.

The Golden Rule of Crochet Thread Sizing

Here is the single most important rule to remember: 

The higher the size number, the thinner the thread.

Why does it work this way? Thread sizes are derived from the traditional gunze or count system originally used in textile manufacturing, which measures thread weight based on length relative to mass. To simplify: Size 3 is thick, Size 10 is medium, and Size 30 or higher is ultra-fine.

Recommended Hook Sizes

Because thread gets thinner as numbers go up, the hook sizes follow the exact same inverse rule: the larger the hook number, the smaller the crochet thread size.