Crochet hook sizes
Millimetres, US letters and UK numbers for every common hook, plus the yarn weight each one suits. The chart to check before you start, and after the marking has worn off.
Three systems describe the same hooks. Millimetres measure the shaft directly, US sizes use a letter and a number, and UK sizes use a number that runs the opposite way, where larger numbers mean smaller hooks. A pattern might name any of them.
Millimetres are the only one that is genuinely unambiguous, so when you are recording what you own or buying a replacement, that is the number worth trusting.
Hook conversion chart
| Metric | US | UK | Typical yarn |
|---|---|---|---|
| 2.0 mm | no equivalent size | 14 | Lace / thread |
| 2.25 mm | B-1 | 13 | Lace, fine thread |
| 2.5 mm | no equivalent size | 12 | Fingering |
| 2.75 mm | C-2 | 11 | Fingering / 4-ply |
| 3.0 mm | no equivalent size | 11 | Fingering / sport |
| 3.25 mm | D-3 | 10 | Sport |
| 3.5 mm | E-4 | 9 | Sport / DK |
| 3.75 mm | F-5 | no equivalent size | DK |
| 4.0 mm | G-6 | 8 | DK / light worsted |
| 4.5 mm | 7 | 7 | Worsted |
| 5.0 mm | H-8 | 6 | Worsted / aran |
| 5.5 mm | I-9 | 5 | Aran |
| 6.0 mm | J-10 | 4 | Aran / chunky |
| 6.5 mm | K-10½ | 3 | Chunky |
| 8.0 mm | L-11 | 0 | Chunky / bulky |
| 9.0 mm | M/N-13 | 00 | Super bulky |
| 10.0 mm | N/P-15 | 000 | Super bulky |
| 12.0 mm | no equivalent size | no equivalent size | Jumbo |
| 15.0 mm | P/Q | no equivalent size | Jumbo / arm crochet |
| 25.0 mm | U | no equivalent size | Jumbo roving |
The yarn column is a starting point rather than a rule. Yarn bands carry their own recommendation, and the fabric you want matters more than either.
Hook size decides fabric, not just size
It is tempting to treat hook size as a way of making things bigger or smaller. It does that, but the more important effect is on the fabric itself. A larger hook with the same yarn gives a looser, drapier fabric with more visible gaps. A smaller hook gives something denser and stiffer.
Which is right depends entirely on what you are making:
- Amigurumi needs dense fabric so stuffing does not show through. Go a size or two below the band's suggestion.
- Blankets and shawls usually want drape, so the band's suggestion or a size up works well.
- Garments should match the pattern's gauge, because the finished measurements depend on it.
- Bags want a firm fabric that holds its shape, so err smaller.
Gauge beats the label
If your gauge square does not match the pattern, change hook size rather than trying to crochet tighter or looser. Tension you have to maintain deliberately will not survive a whole blanket, and the size will drift.
Working out what an unmarked hook is
Printed sizes wear off aluminium hooks, and ergonomic handles often hide the marking entirely. The traditional answer is a hook gauge, a plate with holes you slide the shaft into. Yarnova includes a hook and needle gauge in its tool kit that does the same on screen.
Once you have identified a hook, the useful next step is recording it in your stash, so the next time you wonder whether you own a 4.5mm you can check instead of guessing. Duplicate hooks are the most commonly re-bought crochet item precisely because this is hard to remember.
Steel hooks are a separate scale
Thread and lace work uses steel hooks, numbered on their own system where higher numbers mean smaller hooks, the reverse of what you might expect. A steel size 7 is around 1.65 mm. If a pattern calls for thread and a numbered steel hook, it is not the same scale as the chart above.
Once you have the right hook and the right yarn, the abbreviations guide covers reading the pattern itself.