A 4.5mm crochet hook has no single standard US letter. This size causes more confusion than almost any other because of that gap: some brands print nothing but the mm size, others stamp a “7” on it, and neither is wrong. If a pattern just says “size 7” without a mm measurement, double check it means 4.5mm and not something else before starting.
What is a 4.5mm crochet hook used for?
This size sits between a 4mm (G-6) and a 5mm (H-8), which is exactly why manufacturers never agreed on a letter for it. It suits light worsted and DK weight yarn best, giving a slightly looser fabric than a 4mm hook in the same yarn.
- Yarn weight: DK to light worsted.
- Common projects: amigurumi in finer yarn, lightweight garments, baby items.
How 4.5mm compares to nearby sizes
Switching to 4.5mm from a 4mm hook helps whenever a pattern feels too tight or stiff at 4mm, since the jump in drape is noticeable even though the size difference is small. Going up to 5mm instead produces a visibly looser, more open fabric than most patterns intend for this weight.
Frequently asked questions
What letter is a 4.5mm crochet hook?
There is no universal US letter for 4.5mm. Some brands print a “7” on the handle, but most simply mark it by mm size, so go by the mm number rather than a letter for this one.
Can I use a 4.5mm hook instead of a 5mm hook?
You can, but expect a slightly tighter, denser fabric than the pattern intended. For anything where exact sizing matters, like a garment, swatch first to check your gauge still matches.
What yarn weight uses a 4.5mm hook?
DK and light worsted weight yarn most commonly call for a 4.5mm hook, though gauge always matters more than the label.
See the full hook size chart
Compare 4.5mm against every other mm, US, and UK size in one table.