Crochet hooks carry US letter and number labels alongside metric sizes, plus an older UK system. This chart compares all three.
| Metric (mm) | US | UK |
|---|---|---|
| 2.0 | — | 14 |
| 2.25 | B-1 | 13 |
| 2.75 | C-2 | — |
| 3.25 | D-3 | 10 |
| 3.5 | E-4 | 9 |
| 4.0 | G-6 | 8 |
| 4.5 | 7 | 7 |
| 5.0 | H-8 | 6 |
| 5.5 | I-9 | 5 |
| 6.0 | J-10 | 4 |
| 6.5 | K-10.5 | 3 |
See the Hook Size Converter and the Crochet Hook Size Chart.
The calculators and tools on Formula Factory are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. Formula Factory makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.
