Every crochet hook in mm and US letter-number (B-1 to S), with the yarn weights each one is meant for.
How it works
Crochet hooks are sold by their shaft diameter in millimeters. US hooks also carry a letter and a number (H-8 is 5 mm), but brands differ a little, so the millimeter size is the one to trust.
Each yarn weight has a recommended hook range: worsted (4) uses 5.5–6.5 mm (I-9 to K-10½), DK (3) 4.5–5.5 mm, bulky (5) 6.5–9 mm. Amigurumi goes 1–2 sizes smaller for a tight fabric.
Pick a hook to see its US size, the yarn weights it suits and the knitting needle of the same size.
Frequently asked questions
What size is an H crochet hook?
An H-8 hook is 5 mm. The Craft Yarn Council lists it for light yarn (DK, light worsted); many crocheters also use it with worsted for a firmer fabric.
What size is a J hook in mm?
A J-10 hook is 6 mm, a common size for worsted weight yarn.
What hook do I use for worsted weight yarn?
The Craft Yarn Council suggests 5.5–6.5 mm: I-9, J-10 or K-10½. Go smaller for amigurumi.