Crochet Hook Sizes Chart: US Letters to mm

Q: What size is a G hook?

A G-6 hook is 4 mm. Some brands also sell a 4.25 mm G.

Q: What mm is an I-9 hook?

An I-9 hook is 5.5 mm. A plain I without the 9 is 5.25 mm.

Q: What size is a J hook?

A J-10 hook is 6 mm. A plain J is 5.75 mm.

Crochet hook sizes, US and metric

Crochet hook sizes in millimetres and US letters
Millimetres	US size
2.25 mm	B-1
2.5 mm	no US size
2.75 mm	C-2
3.125 mm	D
3.25 mm	D-3
3.5 mm	E-4
3.75 mm	F-5
4 mm	G-6
4.25 mm	G
4.5 mm	7
5 mm	H-8
5.25 mm	I
5.5 mm	I-9
5.75 mm	J
6 mm	J-10
6.5 mm	K-10 1/2
7 mm	no US size
8 mm	L-11
9 mm	M/N-13
10 mm	N/P-15
11.5 mm	P-16
12 mm	no US size
15 mm	P/Q
15.75 mm	Q
16 mm	Q
19 mm	S
25 mm	T/U/X
30 mm	T/X

Which hook for which yarn

Recommended hook by yarn weight
Yarn weight	Hook, mm	Hook, US	Single crochet per 4 in
0 Lace	steel 1.4 to 1.6 mm, regular 2.25 mm	steel 6, 7, 8; regular B-1	32 to 42 dc
1 Super Fine	2.25 to 3.5 mm	B-1 to E-4	21 to 32
2 Fine	3.5 to 4.5 mm	E-4 to 7	16 to 20
3 Light	4.5 to 5.5 mm	7 to I-9	12 to 17
4 Medium	5.5 to 6.5 mm	I-9 to K-10 1/2	11 to 14
5 Bulky	6.5 to 9 mm	K-10 1/2 to M-13	8 to 11
6 Super Bulky	9 to 15 mm	M-13 to Q	7 to 9
7 Jumbo	15 mm and larger	Q and larger	6 and fewer

The Craft Yarn Council calls these guidelines only. Lace weight gauge is given in double crochet.

Steel hooks run backwards

Steel hooks for thread are sized the other way round: the higher the number, the smaller the hook. The smallest steel hook is a 14 at 0.9 mm and the largest is a 00 at 2.7 mm.

Always swatch

If your swatch is bigger than the pattern gauge, go down a hook size. If it is smaller, go up. The same letter can be a different size from one brand to the next, so match by millimetres.

Sources

Craft Yarn Council, Hooks & Needles and Standard Yarn Weight System. https://www.craftyarncouncil.com/standards/hooks-and-needles

Common questions

What size is an H hook in mm?

An H-8 hook is 5 mm.

What size is a G hook?

A G-6 hook is 4 mm. Some brands also sell a 4.25 mm G.

What mm is an I-9 hook?

An I-9 hook is 5.5 mm. A plain I without the 9 is 5.25 mm.

What size is a J hook?

A J-10 hook is 6 mm. A plain J is 5.75 mm.

What hook should I use for worsted weight yarn?

The Craft Yarn Council recommends 5.5 to 6.5 mm (I-9 to K-10 1/2) for medium weight 4 yarn. Check the yarn label and your gauge swatch.

Why does the same letter have two sizes?

Letters and numbers vary from company to company. The Craft Yarn Council advises relying on the millimetre size printed on the package.