crochetCrochet hook size converter
Start with millimeters. US letters and old UK numbers are useful labels, but they are not identical across every brand.
Your hook size
US H-8 · old UK 6
Match the diameter printed on the hook or package.
Why a letter is not always enough
A US G hook may be 4.0 or 4.25 mm. Historic UK charts also disagree on some small sizes. When more than one match appears, use the millimeter marking on the hook or the pattern designer's gauge. A larger hook generally makes larger stitches, but make a swatch to test the fabric.
Regular crochet hook chart
| Millimeters | US | Old UK |
|---|---|---|
| 2 mm | No standard label | 14 (old) |
| 2.25 mm | B-1 | 13 (old) |
| 2.5 mm | No standard label | 12 (old, sometimes blank) |
| 2.75 mm | C-2 | 12 or 11 (old) |
| 3 mm | No standard label | 11 (old) |
| 3.125 mm | D | No consistent label |
| 3.25 mm | D-3 | 10 (old) |
| 3.5 mm | E-4 | 9 (old) |
| 3.75 mm | F-5 | 9 or blank (old) |
| 4 mm | G-6 | 8 (old) |
| 4.25 mm | G | No consistent label |
| 4.5 mm | 7 | 7 (old) |
| 5 mm | H-8 | 6 (old) |
| 5.25 mm | I | No consistent label |
| 5.5 mm | I-9 | 5 (old) |
| 5.75 mm | J | No consistent label |
| 6 mm | J-10 | 4 (old) |
| 6.5 mm | K-10.5 | 3 (old) |
| 7 mm | No standard label | 2 (old, chart-dependent) |
| 8 mm | L-11 | 0 (old) |
| 9 mm | M/N-13 | 00 (old) |
| 10 mm | N/P-15 | 000 (old) |
| 11.5 mm | P-16 | No consistent label |
| 12 mm | No standard label | No consistent label |
| 15 mm | P/Q | No consistent label |
| 15.75 mm | Q | No consistent label |
| 16 mm | Q | No consistent label |
| 19 mm | S | No consistent label |
| 25 mm | T/U/X | No consistent label |
| 30 mm | T/X | No consistent label |
Steel hooks use a different scale
Steel hooks are usually for crochet thread and lace. Their numbers often get larger as the diameter gets smaller. A steel number 10 is not a 10 mm yarn hook. Even steel numbering differs between brands; this tool shows CYC-listed matches, not a promise that your hook uses the same scale.