Crochet Hook Size Converter

Convert crochet hook sizes between millimetres, US letters and numbers, old UK/Canadian sizes and Japanese sizes. Includes steel thread hooks.

Crochet hook size conversion
Metric	US	UK / CA (old)	Japan
2 mm	–	14	2/0
2.25 mm	B-1	13	3/0
2.5 mm	–	12	4/0
2.75 mm	C-2	–	–
3 mm	–	11	5/0
3.25 mm	D-3	10	–
3.5 mm	E-4	9	6/0
3.75 mm	F-5	–	–
4 mm	G-6	8	7/0
4.5 mm	7	7	7.5/0
5 mm	H-8	6	8/0
5.5 mm	I-9	5	9/0
6 mm	J-10	4	10/0
6.5 mm	K-10.5	3	–
7 mm	–	2	7 mm
8 mm	L-11	0	8 mm
9 mm	M/N-13	00	–
10 mm	N/P-15	000	10 mm
11.5 mm	P-16	–	–
12 mm	–	–	12 mm
15 mm	P/Q	–	–
16 mm	Q	–	–
19 mm	S	–	–
25 mm	T/U/X	–	–

Steel crochet hooks (thread)

Steel hook numbers run backwards: the higher the number, the smaller the hook.

Metric	US steel
3.5 mm	Steel 00
3.25 mm	Steel 0
2.75 mm	Steel 1
2.25 mm	Steel 2
2.1 mm	Steel 3
2 mm	Steel 4
1.9 mm	Steel 5
1.8 mm	Steel 6
1.65 mm	Steel 7
1.5 mm	Steel 8
1.4 mm	Steel 9
1.3 mm	Steel 10
1.1 mm	Steel 11
1 mm	Steel 12
0.85 mm	Steel 13
0.75 mm	Steel 14

Manufacturers differ slightly (for example some label 4.5 mm as US 7 and others skip it). The millimetre size is the reliable number — it is printed on almost every hook.

Which hook for which yarn?

See the yarn weight chart for the recommended hook range for each yarn weight.

Questions

What size is an H crochet hook?

An H-8 crochet hook is 5 mm. It is the most common hook for worsted-weight yarn.

What is a G hook in mm?

A G-6 hook is 4 mm.

Are UK and US crochet hook sizes the same?

No. The old UK/Canadian system numbers hooks the other way round (a UK 6 is 5 mm, a US H-8). Modern UK hooks are labelled in millimetres, which is the safest size to go by.

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