A 4.5mm crochet hook has no single standard US letter (no standard US letter, usually just called by its mm size). I keep the mm number as my main reference for this size, since letter labeling is where most of the confusion happens between brands.
4.5mm to US letter, UK, and yarn weight
A 4.5mm crochet hook has no single standard US letter (no standard US letter, usually just called by its mm size). It’s typically used for DK to worsted weight yarn, and I check the mm stamp on the hook itself whenever a pattern’s letter doesn’t match what I expect.
What projects use a 4.5mm hook
Match DK to worsted 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. I always swatch first for anything that needs to fit.
Frequently asked questions
Is 4.5mm the same as a lettered size?
A 4.5mm crochet hook has no single standard US letter (no standard US letter, usually just called by its mm size).
What size yarn goes with a 4.5mm hook?
Dk to worsted weight yarn is the usual match for this size.
See the full hook size chart
Compare 4.5mm against every other mm, US, and UK size in one table.