Crochet hook size converter
Convert crochet hook sizes between US letters, US numbers and millimeters.
That's 1.11× as thick as the hook for DK yarn, while the hook for worsted yarn is 1.1× thicker.
What it means
Which yarn suits that hook?
Steel hooks for thread use a separate, reversed numbering and are not covered here. Brands differ slightly above 6 mm.
Every unit
That hook in every system
Learn
Three things worth knowing
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H-8 is 5 mm
The most common hook. G-6 is 4 mm, I-9 is 5.5 mm and J-10 is 6 mm.
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Letters came first
American hooks were labeled with letters long before the metric size was stamped on them; the number was added later so the letters could be put in order.
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Two hooks called N
Some brands call the 9 mm hook M/N-13 and the 10 mm hook N/P-15. Check the millimeters before buying.
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Popular hook size conversions
Background
About crochet hook sizes
A hook is sized by the diameter of its shaft in millimeters. US hooks add a letter and a number: H-8 is 5 mm, G-6 is 4 mm, K-10½ is 6.5 mm.
Type a letter like H or K in the US letter box and it converts too. The 4.5 mm hook is the odd one out: it is sold as a plain US 7, with no letter.