Crochet hooks are labeled differently around the world: metric millimeters, US letters and numbers, and old UK numbers. This chart lines them all up so you can always find the right hook — whatever a pattern asks for.
Crochet hook conversion chart
| Metric (mm) | US size | Old UK size | Common use |
|---|---|---|---|
| 2.25 mm | B-1 | 13 | Fine (#1) yarn, small amigurumi |
| 2.75 mm | C-2 | 12 | Fine (#1) yarn |
| 3.25 mm | D-3 | 10 | Fine–sport yarn |
| 3.5 mm | E-4 | 9 | Sport (#2) yarn |
| 3.75 mm | F-5 | — | Sport–DK yarn |
| 4 mm | G-6 | 8 | DK (#3) yarn, amigurumi |
| 4.5 mm | 7 | 7 | DK (#3) yarn |
| 5 mm | H-8 | 6 | Worsted (#4) yarn — great for beginners |
| 5.5 mm | I-9 | 5 | Worsted (#4) yarn |
| 6 mm | J-10 | 4 | Worsted–aran yarn |
| 6.5 mm | K-10½ | 3 | Aran–bulky (#5) yarn |
| 8 mm | L-11 | 0 | Bulky (#5) yarn |
| 9 mm | M/N-13 | 00 | Bulky–super bulky (#6) yarn |
| 10 mm | N/P-15 | 000 | Super bulky (#6) yarn |
| 15 mm | P/Q | — | Super bulky (#6) yarn |
| 16 mm | Q | — | Super bulky–jumbo yarn |
| 19 mm | S | — | Jumbo (#7) yarn |
| 25 mm | T/U/X | — | Jumbo (#7) yarn |
Always trust the millimeter size. Letter and number labels can vary between brands, but the metric size is the actual diameter of the hook shaft.
Steel hooks for thread crochet
Very small steel hooks are used with crochet thread for lace, doilies and fine details. Their numbers work in reverse: the bigger the number, the smaller the hook. For example, a US steel size 7 is about 1.65 mm, while a steel size 10 is about 1.3 mm. Check the millimeter size printed on the hook when following a thread pattern.
How to choose the right hook
- Start with the hook size recommended on your yarn label.
- Check the pattern — it may ask for a smaller hook for firmer fabric (amigurumi) or a larger hook for drape (shawls).
- Make a gauge swatch. Too many stitches? Go up a size. Too few? Go down a size.
- Try different handles: inline vs tapered heads and ergonomic grips feel very different in the hand.
See also: Yarn weight chart · Crochet abbreviations