1 · ON YOUR HOOK
Look for millimeters
The size is often stamped on the flat grip or handle. This example reads 5.5 mm; choose that number above if your hook has it.
FREE CROCHET HOOK SIZE TOOL
Crochet hook size chart & converter.
Match US labels to millimeters, compare a hook with your yarn, or go straight to the full size chart.
WHAT DO YOU HAVE?
What does your hook say?
If both markings appear, use millimeters; US labels can differ by maker. Where is the size marked?
Reference: Craft Yarn Council · reviewed September 23, 2026.
EXAMPLE · CHOOSE ABOVEREGULAR YARN HOOKS
6mm≈J-10US
J-10 is the US label paired with 6 mm in the reference.
SmallerLarger
Nearby: 5.75 mm (J)6.5 mm (K-10½)
If your pattern names a hook size, start there. Does your practice square match?
SAVE THIS REFERENCE
Crochet hook size chart: US ↔ mm
Find a size at a glance, or tap “Use” to see it in the converter. Millimeters are the safer match when US markings differ by maker.
| Millimeters | US label | Choose size |
|---|---|---|
| 2.25 mm | B-1 | |
| 2.5 mm | — | |
| 2.75 mm | C-2 | |
| 3.125 mm | D | |
| 3.25 mm | D-3 | |
| 3.5 mm | E-4 | |
| 3.75 mm | F-5 | |
| 4 mm | G-6 | |
| 4.25 mm | G | |
| 4.5 mm | 7 | |
| 5 mm | H-8 | |
| 5.25 mm | I | |
| 5.5 mm | I-9 | |
| 5.75 mm | J |
| Millimeters | US label | Choose size |
|---|---|---|
| 6 mm | J-10 | |
| 6.5 mm | K-10½ | |
| 7 mm | — | |
| 8 mm | L-11 | |
| 9 mm | M/N-13 | |
| 10 mm | N/P-15 | |
| 11.5 mm | P-16 | |
| 12 mm | — | |
| 15 mm | P/Q | |
| 15.75 mm | Q | |
| 16 mm | Q | |
| 19 mm | S | |
| 25 mm | T/U/X | |
| 30 mm | T/X |
A dash means the Craft Yarn Council reference lists no US label for that millimeter size. This chart is for regular yarn hooks, not steel/thread hooks.
IF YOUR SQUARE DOESN’T MATCH
Which hook should you try next?
Compare the stitch count across the same 4-inch (10 cm) width in your pattern and practice square. Count in the middle, away from uneven edges.
For example: pattern 16 stitches, your square 18 stitches → try a larger hook.
Enter two whole stitch counts from 1 to 100 to see a suggestion.
Use the same yarn and stitch pattern for a fair comparison. This is a direction to try, not an exact size calculation. Gauge guidance: Craft Yarn Council.
WHERE TO LOOK
Find the number on what you already have
2 · ON YOUR YARN
Find the yarn number
Look for a numbered yarn-ball symbol on the wrapper. 4 means medium-weight yarn; the label’s own hook advice and your pattern still come first.
Illustrative examples; markings and labels differ by manufacturer.
BEFORE YOU START
What changes with a different hook?
Choose a smaller hook
Stitches may become tighter and the fabric firmer. Your finished size can change.
Choose a larger hook
Stitches may become looser and the fabric more open. Check your pattern’s measurements.
These are general tendencies, not a prediction for a particular pattern or yarn.
METHOD
Why millimeters come first
The Craft Yarn Council notes that US letter and number labels vary across manufacturers. We use its published millimeter-to-US reference, leaving a US label blank when its table does. We never convert steel/thread hooks using the standard-yarn-hook table.
The yarn selector uses the Council’s recommended hook ranges by yarn weight. Its ranges are guidelines. Your yarn label, pattern instruction and gauge swatch are the final checks.
How this reference is checked
Each size pair and yarn range is compared with the linked Council tables. A missing US label stays blank; a shared label shows all listed millimeter sizes instead of guessing. The tool does not measure a physical hook or predict your personal stitch tension.
Who maintains this tool?
Hook Size Studio is built and maintained by Virtual Persona Studios. To report a wrong size, a broken link or an accessibility problem, email admin@virtualpersonastudios.com. We check corrections against the cited sources before changing the reference.
Sources reviewed September 23, 2026. This tool does not recommend a particular brand or product.
QUICK ANSWERS
Before you pick up your yarn
Where do I find my yarn’s number?
Check the paper label around your yarn. Many labels show a little yarn-ball symbol with a number from 0 to 7. This tool covers categories 1 to 7; for category 0, follow your pattern and yarn label.
What is a practice square?
It is a small sample made with your yarn and hook before the full project. Compare its stitch size with your pattern. If the sample is too small, try a larger hook; if it is too large, try a smaller one.
Is a US letter always the same millimeter size?
No. Manufacturers can differ, so the millimeter marking is the more reliable measurement. When a label is ambiguous, check the package or measure the hook.
Can I use this chart for steel crochet hooks?
No. Steel/thread hooks follow a different numbering convention. This tool covers regular yarn hooks only.
What if my pattern names a different hook?
Start with the pattern’s instruction and make a small practice square. Adjust only after comparing it with the pattern’s measurements.