5.5 mm crochet hook
A 5.5 mm hook is a US size I/9, UK 5, and 9/0号 in Japan. Buy by the millimetre number — it's printed on every hook and it means the same thing everywhere.
Worsted to aran, scarves and blankets.
The same hook in every system
| Millimetres (the one that always works) | 5.5 mm |
|---|---|
| US | I/9 |
| UK | 5 |
| Japanese 号 | 9/0号 |
| Type | standard |
Yarn weights that suit this hook
2 standard yarn weights list 5.5 mm inside their recommended hook range. Expected single crochet gauge over 4 inches is shown as a range — the CYC figures assume a mid-range hook, so at 5.5 mm you will land toward the loose end. Swatch before you commit.
Aluminium, ergonomic and Japanese-style options in this size.
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Nearby sizes
All hook sizes · US to Japanese hook chart
Last updated 2026-08-30.