A crochet hook size is read in millimeters: it's the diameter of the shaft, the only measurement that's the same in every country. The US letters and numbers (B-1, G-6, H-8…) refer to those diameters under the Craft Yarn Council standard. So an English pattern that calls for an H-8 hook is crocheted with a 5 mm.
Which crochet hook size matches a US size?
| Millimeters | US size |
|---|---|
| 2.25 mm | B-1 |
| 2.5 mm | — |
| 2.75 mm | C-2 |
| 3.125 mm | D |
| 3.25 mm | D-3 |
| 3.5 mm | E-4 |
| 3.75 mm | F-5 |
| 4 mm | G-6 |
| 4.25 mm | G |
| 4.5 mm | 7 |
| 5 mm | H-8 |
| 5.25 mm | I |
| 5.5 mm | I-9 |
| 5.75 mm | J |
| 6 mm | J-10 |
| 6.5 mm | K-10 ½ |
| 7 mm | — |
| 8 mm | L-11 |
| 9 mm | M/N-13 |
| 10 mm | N/P-15 |
| 11.5 mm | P-16 |
| 12 mm | — |
| 15 mm | P/Q |
| 15.75 mm | Q |
| 16 mm | Q |
| 19 mm | S |
| 25 mm | T/U/X |
| 30 mm | T/X |
A dash means a size with no US equivalent. The old UK and Canadian sizes (numbers 14 to 000) vary from one maker to another: go by the millimeters printed on the handle.
Which crochet hook size for which yarn?
| Yarn category | Common names | Recommended hook | US size |
|---|---|---|---|
| 0 — Lace | fingering, crochet thread size 10 | 1.4 to 1.6 (steel) or 2.25 mm | steel 6, 7, 8 or B-1 |
| 1 — Super fine | sock, fingering, baby | 2.25 to 3.5 mm | B-1 to E-4 |
| 2 — Fine | sport, baby | 3.5 to 4.5 mm | E-4 to 7 |
| 3 — Light | DK, light worsted | 4.5 to 5.5 mm | 7 to I-9 |
| 4 — Medium | worsted, afghan, aran | 5.5 to 6.5 mm | I-9 to K-10 ½ |
| 5 — Bulky | chunky, craft, rug | 6.5 to 9 mm | K-10 ½ to M-13 |
| 6 — Super bulky | super bulky, roving | 9 to 15 mm | M-13 to Q |
| 7 — Jumbo | jumbo, roving | 15 mm and up | Q and up |
The category is often printed on the yarn label, inside a little ball of yarn numbered 0 to 7. The label also shows the hook recommended by the manufacturer: that takes priority over this chart.
Frequently asked questions
Which crochet hook size should a beginner use?
With a medium yarn (category 4), the recommended hook goes from 5.5 to 6.5 mm: the stitches are big and easy to count.
My work is too tight: what should I change?
Go up one hook size in the chart; too loose, go down one size. The gauge in the pattern tells you whether that's fixed the difference.
Sources: Craft Yarn Council standards, crochet hook sizes and yarn weight categories, checked on 07/10/2026. Chart free to reuse, with a link to this page.