Crochet hook size to mm (US letter sizes)
American patterns give hooks as a letter and number; this tool gives the millimeter size printed on hooks.
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How to use it
- Enter us size.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
There is no formula; each US size maps to a set diameter in the Craft Yarn Council chart for standard hooks, for example H-8 = 5 mm.
Example
Inputs: US size = H-8. Result: Hook diameter: 5 mm; Diameter in inches: 0.197 in.
Limits and caveats
- This chart covers standard yarn hooks up to 10 mm; steel lace hooks use a different numbering.
- Some brands use different letters for the 9 mm and 10 mm hooks.
Questions about this tool
What is an H-8 crochet hook in mm?
It is 5 mm.
What is a G-6 hook in mm?
It is 4 mm.
Why do some hooks have a number but no letter?
The 4.5 mm hook is just called 7 in the US chart because it has no letter of its own.