Crochet Hook Sizes: The Complete Comparison Chart & How to Choose
US letters vs. millimeters vs. steel sizes — decoded once and for all.
If crochet hook sizing feels like it was designed by three different committees who never spoke to each other — you're not wrong. The US uses letters, most of the world uses millimeters, and thread work has its own steel numbering that runs BACKWARDS. It is a mess. But it's a solvable mess, and by the end of this you'll read any pattern's hook call without flinching.
The master conversion chart
Bookmark this. When a US pattern says ‘H hook’ and your hooks only show millimeters, this is the table that saves the day.
| US Size | Metric (mm) | Common use |
|---|---|---|
| B-1 | 2.25 mm | Fine thread, tight amigurumi |
| C-2 | 2.75 mm | Amigurumi, fingering yarn |
| D-3 | 3.25 mm | Sport yarn, small toys |
| E-4 | 3.5 mm | DK amigurumi, baby items |
| G-6 | 4.0 mm | DK yarn, light garments |
| H-8 | 5.0 mm | Worsted — the everyday hook |
| I-9 | 5.5 mm | Worsted blankets & scarves |
| J-10 | 6.0 mm | Heavy worsted, aran |
| K-10.5 | 6.5 mm | Bulky yarn |
| L-11 | 8.0 mm | Bulky & super bulky |
| N/P | 9–10 mm | Super bulky, chunky throws |
Trust the millimeter, not the letter
Here's a pro habit worth building: always think in millimeters. Letter sizes vary slightly between brands — one company's H might be 5.0 mm and another's 5.25 mm — but a millimeter is a millimeter everywhere on earth. Most quality crochet hooks stamp the mm size right on the handle. When in doubt, that number is the truth.
Steel hooks: the backwards world of thread crochet
If you ever fall down the rabbit hole of doilies and lace — and it's a lovely hole — you'll meet steel crochet hooks. These use their own numbering where BIGGER numbers mean SMALLER hooks. A size 14 steel hook is a tiny needle-like thing for the finest thread, while a size 00 is comparatively chunky. Don't let it rattle you; just check the mm if it's printed.
How to actually choose your hook
Start with the yarn label. Every ball band suggests a hook size, and that suggestion is a genuinely good starting point. From there, adjust for what you’re making:
- Amigurumi: Go DOWN a size or two from the label. Tight stitches keep the stuffing hidden.
- Blankets & wearables: Use the label size, or go up one for softer drape.
- Lacework: Go UP a size to open the stitches and show off the pattern.
- Tension trouble: If you crochet tightly, size up; if you crochet loosely, size down.
Do you really need a full set?
Eventually, yes — but not on day one. A good starter set of ergonomic crochet hooks covering roughly 2.75 mm to 6.5 mm will handle the vast majority of patterns. Add specialty sizes as specific projects demand them. Your hands (and your budget) will thank you for building up gradually.
Comfortable hooks make a genuine difference over a long project — sore hands end more crochet sessions than boredom ever does. See our favorite hook sets and ergonomic picks over in the shop.
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