Crochet Hook Size Converter
Convert crochet hook sizes between metric millimeters, US letters and numbers, UK/Canada sizes, and Japanese sizes. Handy when a yarn label, pattern, or hook uses a different sizing system than you do.
Convert a crochet hook size
Pick the system you know, enter the size, and get the closest matching hook sizes instantly.
A 5 mm hook is commonly labeled US H-8, UK/Canada 6, and Japan 8/0.
How to use crochet hook conversions
- Use millimeters first when your hook has a metric marking; it is the clearest comparison across countries.
- If your pattern lists a US letter, convert it to millimeters before choosing a substitute hook.
- Make a gauge swatch for garments, hats, fitted items, and any project where finished size matters.
- If your gauge has too many stitches per inch, try a larger hook. If it has too few, try a smaller hook.
Quick crochet hook size chart
| Metric | US | UK/Canada | Japan |
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Crochet hook conversion FAQ
Why do crochet hook sizes vary by brand?
Hook sizing systems developed separately, and some brands round differently. The millimeter size stamped on the hook is usually the best reference.
Is a US H hook always 5 mm?
Most modern charts list US H-8 as 5 mm, but older hooks and some brands may differ. If gauge matters, measure or check the hook's metric marking.
Can I substitute a close hook size?
Usually yes for scarves, blankets, and simple projects. For fitted pieces, make a swatch because even a 0.5 mm change can affect finished size.