A 6mm crochet hook is a US J-10. In UK sizing it’s a 4. Use the mm number as your main reference for this size, since letter labeling is where most of the confusion happens between brands.
6mm to US letter, UK, and yarn weight
A 6mm crochet hook is a US J-10. In UK sizing it’s a 4. It’s typically used for chunky weight yarn; check the mm stamp on the hook itself whenever a pattern’s letter doesn’t match what you expect.
What projects use a 6mm hook
Match chunky weight yarn to this hook for the gauge most patterns expect, then adjust up or down a size if your own tension runs tight or loose. Swatch first for anything that needs to fit.
Frequently asked questions
Is 6mm the same as J-10?
A 6mm crochet hook is a US J-10. In UK sizing it’s a 4.
What size yarn goes with a 6mm hook?
Chunky weight yarn is the usual match for this size.
See the full hook size chart
Compare 6mm against every other mm, US, and UK size in one table.