Hook size

6 mm crochet hook

A 6 mm crochet hook equals US size J-10 and has old UK size 4. It is the recommended hook range for medium (4) yarn, and crocheters typically choose it for worsted-weight blankets, scarves and relaxed-drape garments. Always check gauge with a swatch, because tension varies between crocheters.

By the crochetpatterns.io editorial team · Reviewed September 13, 2026 · Editorial policy

6 mm crochet hook conversions
Metric	US	Old UK	Suits yarn weights
6 mm	J-10	4	#4 Medium

What is a 6 mm crochet hook in US and UK sizes?

A 6 mm hook is US size J-10 and old UK size 4. Metric millimetres are the only measurement that is the same on every brand, so check the mm size stamped on the hook.

Hook sizes around 6 mm
Metric	US	Old UK	Yarn weights
5 mm	H-8	6	#3
5.5 mm	I-9	5	#3, #4
6 mm (this hook)	J-10	4	#4
6.5 mm	K-10½	3	#4, #5
7 mm	—	2	#5

What yarn weight goes with a 6 mm hook?

A 6 mm hook is typically used with medium (#4) yarn. Medium yarn gives about 11–14 sc per 4 in / 10 cm and suits blankets and afghans, beanies, granny squares.

Yarn weights for a 6 mm hook
Weight	Also called	Crochet gauge	Recommended hooks
#4 Medium	Worsted, Afghan, Aran, 10-ply (AU/NZ)	11–14 sc per 4 in / 10 cm	5.5–6.5 mm

What can you make with a 6 mm hook?

7 patterns in our library use a 6 mm hook, including flame crochet scarf and hat, flings ’n caps lace hat and scarf set, two-toned reversible afghan (1951), wilshire shell stitch stole (1951), boldly banded man's crochet jacket, bulky yarn afghan (vintage crazy daisy).