Crafts & Sewing
Crochet hook conversion
Crochet hook size equivalents mm ↔ US ↔ UK.
- Instant
- Free
- Private (processed locally)
- No sign-up
Convert a crochet hook size
Enter the diameter in mm: the closest row is highlighted in the mm ↔ US ↔ UK chart.
Good to know
- mm is the reliable reference
- US letters vary by brand
- UK numbers decrease as mm increases
- Confirm with your gauge swatch
Some equivalents
| mm | US | UK |
|---|---|---|
| 3.5 | E-4 | 9 |
| 4.0 | G-6 | 8 |
| 5.0 | H-8 | 6 |
| 6.0 | J-10 | 4 |
Indicative equivalents. 100% local, no data sent.
Frequently asked questions
Is the mm system universal?
Yes, the diameter in millimetres is the most reliable reference, since US letters and UK numbers vary by brand.
What is a 5 mm hook?
Roughly a US H-8 and a UK 6. The tool highlights it automatically.
Why do equivalents differ?
Letter/number mappings are not standardised; always trust the mm engraved on the hook.
What about steel (thread) hooks?
They use a different numbering (very small diameters); this chart covers standard hooks.