Crochet Hook Size Converter — mm, US & UK
Convert any crochet hook size between metric (mm), US letters/numbers, and UK/Canada.
| Metric (mm) | US | UK / Canada |
|---|---|---|
| 2.25 mm | B-1 | 13 |
| 2.5 mm | — | 12 |
| 2.75 mm | C-2 | 11 |
| 3.0 mm | — | 10 |
| 3.25 mm | D-3 | 10 |
| 3.5 mm | E-4 | 9 |
| 3.75 mm | F-5 | — |
| 4.0 mm | G-6 | 8 |
| 4.5 mm | 7 | 7 |
| 5.0 mm | H-8 | 6 |
| 5.5 mm | I-9 | 5 |
| 6.0 mm | J-10 | 4 |
| 6.5 mm | K-10½ | 3 |
| 7.0 mm | — | 2 |
| 8.0 mm | L-11 | 0 |
| 9.0 mm | M/N-13 | 00 |
| 10.0 mm | N/P-15 | 000 |
| 12.0 mm | O-16 | — |
| 15.0 mm | P/Q | — |
| 16.0 mm | Q | — |
| 19.0 mm | S | — |
No hook size matches “”. Try a millimetre value like 5.0.
How to use this tool
- Type any hook size you know — a metric value (5.0), a US size (H-8), or a UK size (6).
- The table filters instantly to the matching row.
- Read across to find the equivalent size in the other systems.
Tip: the millimetre (mm) size is the universal reference — it is identical everywhere in the world. When a pattern lists a US or UK letter, match it to the mm value to be sure you are using the right hook.
Frequently asked questions
How do I convert crochet hook sizes between US and UK?
Use the metric (mm) size as the common reference — it is the same worldwide. For example, a US H/8 hook is 5.0 mm, which is a UK size 6. Search any size in this converter and it shows the matching mm, US, and UK values.
Are US and UK crochet hook sizes the same?
No. The UK/Canada system runs in the opposite direction to the US system (a larger UK number is a smaller hook). Always match by the millimetre size to be safe.
What hook size should a beginner use?
A 5.0 mm (US H/8) or 5.5 mm (US I/9) hook with worsted weight yarn is the easiest combination for beginners — the stitches are large enough to see clearly.
Ready to start a project?
Browse our beginner-friendly crochet PDF patterns — clear photo instructions and instant download.