Crochet Hook Size Converter
Convert crochet hook sizes between metric millimeters and US letter-number sizes such as H-8 and J-10.
How to use the Crochet Hook Size Converter
- Choose metric or US.
- Enter the size (e.g. 5 or H-8).
- Read the equivalent.
How it works
Crochet hooks are measured by shaft diameter in millimeters; the US system adds a letter and number. Standards follow the Craft Yarn Council: 5 mm = H-8, 6 mm = J-10, 4 mm = G-6. Brands sometimes differ slightly, so the millimeter size printed on the hook is the one to trust. Steel thread hooks use a separate numbering where higher numbers are smaller.
Frequently asked questions
What is an H hook in mm?
5 mm (H-8).
What hook size for worsted yarn?
Usually 5–5.5 mm (H-8 to I-9).
What is a 6 mm crochet hook in US?
J-10.
What size is a G hook?
4 mm (G-6).
What is the difference between US and UK crochet hooks?
The US uses letters and numbers (H-8), the UK now uses millimeters, and old UK sizes ran in reverse numbers — always compare millimeter sizes.
What hook size for chunky yarn?
Usually 6.5–9 mm (K-10½ to M/N-13).