Crochet techniques
Crochet Hook Sizes Chart: US Letters to Millimeters
Use the millimeter diameter as the common measurement when a pattern and your tool use different sizing systems. The numbers are labels, not a scale you can convert by multiplying. A size conversion identifies a tool; it does not guarantee the pattern's gauge.
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Find the size you need
For example, H-8 is 5 mm, I-9 is 5.5 mm and J-10 is 6 mm in this reference. Makers sometimes use a different diameter for the same letter: when two tools disagree, compare the stamped millimeters.
| Metric diameter | US size |
|---|---|
| 2.25 mm | B-1 |
| 2.75 mm | C-2 |
| 3.25 mm | D-3 |
| 3.5 mm | E-4 |
| 3.75 mm | F-5 |
| 4 mm | G-6 |
| 4.5 mm | 7 |
| 5 mm | H-8 |
| 5.5 mm | I-9 |
| 6 mm | J-10 |
| 6.5 mm | K-10½ |
| 8 mm | L-11 |
| 9 mm | M/N-13 |
| 10 mm | N/P-15 |
| 11.5 mm | P-16 |
| 15 mm | P/Q |
| 16 mm | Q |
| 19 mm | S |
| 25 mm | T/U/X |
| 30 mm | T/X |
Prefer selecting a size? Use the interactive size converter to highlight its equivalents.
Save or print the chart
Check an unmarked hook
- Check the shaft or handle for a millimeter marking, then check the manufacturer's size chart.
- If the hook is completely unmarked, a suitable hook gauge or careful measurement of the working shaft can help. The widest part of the head is not the nominal shaft diameter.
- Swatch before replacing a known hook with the unmarked one. Head shape and grip can change your tension even at the same nominal size.
Size is different from length and material
Diameter controls the size of the loops, but your tension, yarn and technique determine the finished gauge. Steel thread hooks use a separate numbering system and are not included in this chart. Do not apply the lettered yarn-hook chart to a numbered steel hook.
Common conversion questions
Questions
What size is an H crochet hook?
The H-8 size is 5 mm in the Craft Yarn Council reference. Check the metric marking because makers can differ.
Is a 4 mm hook always G-6?
It is G-6 in this reference, but some manufacturers label a different diameter G. Millimeters resolve the ambiguity.
Does this include steel crochet hooks?
No. Steel hooks for thread have a separate numbering system. Use a steel-hook chart or the manufacturer's diameter marking.
Reference sizes: Craft Yarn Council Hooks & Needles.
