A 3mm crochet hook has no single standard US letter (between a C-2 (2.75mm) and a D-3 (3.25mm), no standard US letter). I keep the mm number as my main reference for this size, since letter labeling is where most of the confusion happens between brands.
3mm to US letter, UK, and yarn weight
A 3mm crochet hook has no single standard US letter (between a C-2 (2.75mm) and a D-3 (3.25mm), no standard US letter). It’s typically used for sport 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 3mm hook
Match sport 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 3mm the same as a lettered size?
A 3mm crochet hook has no single standard US letter (between a C-2 (2.75mm) and a D-3 (3.25mm), no standard US letter).
What size yarn goes with a 3mm hook?
Sport weight yarn is the usual match for this size.
See the full hook size chart
Compare 3mm against every other mm, US, and UK size in one table.