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 this size in mind for sport weight yarn, and it’s one I check by mm first since letter labeling gets inconsistent at this end of the chart.
What is a 3mm crochet hook used for?
This size pairs with sport yarn most often, and the exact fabric it produces depends more on your own tension than the label on the hook. I always swatch a small square before trusting any single size for a project that needs to fit.
- Yarn weight: sport.
- Common projects: match the weight above to garments, amigurumi, or blankets depending on the density you want.
How 3mm compares to nearby sizes
Compared to nearby sizes, a 2.75mm hook (C-2) produces a tighter, denser fabric in the same yarn, while a 3.25mm hook (D-3) opens the fabric up for a looser drape. I pick 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 3mm crochet hook?
There is no universal US letter for 3mm, since between a C-2 (2.75mm) and a D-3 (3.25mm), no standard US letter. I always go by the mm number for this size rather than trust a letter.
What yarn weight uses a 3mm hook?
Sport weight yarn is the usual match for a 3mm hook, though I always trust my own gauge swatch more than the label on any given skein.
See the full hook size chart
Compare 3mm against every other mm, US, and UK size in one table.