A 6mm crochet hook is a US J-10, and UK size 4. It’s a common size for chunky weight yarn; check it by mm first, since letter labeling gets inconsistent at this end of the chart.
What is a 6mm crochet hook used for?
This size pairs with chunky yarn most often, and the exact fabric it produces depends more on your own tension than the label on the hook. Swatch a small square before trusting any single size for a project that needs to fit.
- Yarn weight: chunky.
- Common projects: match the weight above to garments, amigurumi, or blankets depending on the density you want.
How 6mm compares to nearby sizes
Compared to nearby sizes, a 5.5mm hook (I-9) produces a tighter, denser fabric in the same yarn, while a 6.5mm hook (K-10.5) opens the fabric up for a looser drape. Choose between them based on whether a project needs structure or drape. My rule of thumb is to size down for anything that needs to hold stuffing or structure, and size up for anything meant to drape.
Frequently asked questions
What letter is a 6mm crochet hook?
A 6mm hook is a US J-10. In UK and Canadian sizing, the same hook is a 4.
What yarn weight uses a 6mm hook?
Chunky weight yarn is the usual match for a 6mm hook, though a gauge swatch is more reliable than the label on any given skein.
See the full hook size chart
Compare 6mm against every other mm, US, and UK size in one table.