A K crochet hook, also written K-10.5, is 6.5mm. This is one of the letters crocheters ask about often, since patterns list the letter but hooks are usually easiest to double check by mm.
K hook in mm, and what it’s used for
At 6.5mm, a K hook matches chunky to bulky weight yarn. In UK and Canadian sizing, the same hook is a 3, so always convert by mm rather than assume a UK number lines up with a US letter.
How K compares to nearby letters
A J-10 hook sits one step smaller, producing a tighter fabric in the same yarn. There is no standard lettered size directly above this one on the chart. Choose between them based on whether the project needs structure or drape.
Frequently asked questions
Is K-10.5 the same as 6.5mm?
Yes, K and K-10.5 both refer to the same 6.5mm hook in US sizing. The two names are used interchangeably.
What yarn weight is a K hook for?
Chunky to bulky weight yarn is the standard match for a K hook, and it’s the pairing to try first.
See the full hook size chart
Compare K against every other letter, mm, and UK size in one table.