Measure twice, make once
Crochet hook converter
Look up Craft Yarn Council metric and US sizes for regular and steel crochet hooks.
Start with the calculator. Formula, assumptions, and limits are available when you need them.
Before you use this tool
Choose regular or steel hooks first; they use different numbering systems. Read the shaft diameter in millimetres and select it.
For example, a regular 4 mm hook is listed as US G-6. Check the maker’s diameter if a letter or number disagrees, then verify the fabric with a sample.
Method and limits
Limits and rounding
Millimetres are authoritative. US labels vary by manufacturer, steel hooks use a separate reverse-numbered system, and blank US entries mean the CYC table gives no equivalent. Pattern gauge still decides the working size.