Crochet hook sizes: US, UK and mm

Hook sizes are labeled three different ways depending on where the pattern came from, and the letters don’t line up neatly with the numbers. The millimeter measurement is the one that never lies — it’s stamped on the hook itself, so when a pattern and a label disagree, trust the mm.

Regular hooks

The ones you use for normal yarn. A 5.5 mm (US I-9) with medium (4) yarn is the usual place to start learning.

28 sizes, smallest first.
Metric	US	UK
2 mm	—	14
2.25 mm	B-1	13
2.5 mm	—	—
2.75 mm	C-2	12
3 mm	—	11
3.25 mm	D-3	10
3.5 mm	E-4	—
3.75 mm	F-5	9
4 mm	G-6	8
4.25 mm	—	—
4.5 mm	7	7
4.75 mm	—	—
5 mm	H-8	6
5.5 mm	I-9	5
6 mm	J-10	4
6.5 mm	K-10.5	3
7 mm	—	2
7.5 mm	—	—
8 mm	L-11	0
9 mm	M/N-13	00
10 mm	N/P-15	000
12 mm	O	—
15 mm	P/Q	—
16 mm	Q	—
19 mm	S	—
20 mm	—	—
25 mm	T/U/X	—
35 mm	Y	—

Every letter size, in millimeters

American hooks carry a letter and a number — a “G-6” is one hook, not two. Older hooks and older patterns often print only one of the pair, which is half the confusion. The millimeter is the measurement underneath both.

B hook

A US size B-1 crochet hook measures 2.25 mm — so if your hook says 2.25 mm, it is a B. In UK sizing it is a 13.

C hook

A US size C-2 crochet hook measures 2.75 mm — so if your hook says 2.75 mm, it is a C. In UK sizing it is a 12.

D hook

A US size D-3 crochet hook measures 3.25 mm — so if your hook says 3.25 mm, it is a D. In UK sizing it is a 10.

E hook

A US size E-4 crochet hook measures 3.5 mm — so if your hook says 3.5 mm, it is an E. UK sizing has no number for this one.

F hook

A US size F-5 crochet hook measures 3.75 mm — so if your hook says 3.75 mm, it is an F. In UK sizing it is a 9.

G hook

A US size G-6 crochet hook measures 4 mm — so if your hook says 4 mm, it is a G. In UK sizing it is an 8.

7 hook

A US size 7 crochet hook measures 4.5 mm — so if your hook says 4.5 mm, it is a 7. In UK sizing it is a 7.

H hook

A US size H-8 crochet hook measures 5 mm — so if your hook says 5 mm, it is an H. In UK sizing it is a 6.

I hook

A US size I-9 crochet hook measures 5.5 mm — so if your hook says 5.5 mm, it is an I. In UK sizing it is a 5.

J hook

A US size J-10 crochet hook measures 6 mm — so if your hook says 6 mm, it is a J. In UK sizing it is a 4.

K hook

A US size K-10.5 crochet hook measures 6.5 mm — so if your hook says 6.5 mm, it is a K. In UK sizing it is a 3.

L hook

A US size L-11 crochet hook measures 8 mm — so if your hook says 8 mm, it is an L. In UK sizing it is a 0.

M/N hook

A US size M/N-13 crochet hook measures 9 mm — so if your hook says 9 mm, it is an M/N. In UK sizing it is a 00.

N/P hook

A US size N/P-15 crochet hook measures 10 mm — so if your hook says 10 mm, it is an N/P. In UK sizing it is a 000.

O hook

A US size O crochet hook measures 12 mm — so if your hook says 12 mm, it is an O. UK sizing has no number for this one.

P/Q hook

A US size P/Q crochet hook measures 15 mm — so if your hook says 15 mm, it is a P/Q. UK sizing has no number for this one.

Q hook

A US size Q crochet hook measures 16 mm — so if your hook says 16 mm, it is a Q. UK sizing has no number for this one.

S hook

A US size S crochet hook measures 19 mm — so if your hook says 19 mm, it is an S. UK sizing has no number for this one.

T/U/X hook

A US size T/U/X crochet hook measures 25 mm — so if your hook says 25 mm, it is a T/U/X. UK sizing has no number for this one.

Y hook

A US size Y crochet hook measures 35 mm — so if your hook says 35 mm, it is a Y. UK sizing has no number for this one.

Steel hooks (for thread)

Much finer, and numbered the opposite way round — a bigger steel number means a smaller hook. These are for thread crochet and fine lace, not for yarn.

19 sizes. Note the numbering runs backwards.
Metric	US	UK
0.75 mm	14	—
0.85 mm	13	7
1 mm	12	6.5
1.1 mm	11	6
1.25 mm	—	—
1.3 mm	10	5.5
1.4 mm	9	5
1.5 mm	8	4.5
1.65 mm	7	4
1.8 mm	6	3.5
1.9 mm	5	3
2 mm	4	2.5
2.1 mm	3	2
2.25 mm	2	1.5
2.5 mm	—	—
2.75 mm	1	1
3 mm	—	—
3.25 mm	0	0
3.5 mm	00	—

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