Crochet · hook sizes

Crochet hook size conversion.

Millimetre to US hook letter and number, from the Craft Yarn Council chart. For steel hooks and lace thread see the note below.

mm to US crochet hook size

Metric (mm)	US size
2.25 mm	B-1
2.5 mm	no US size listed
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 listed
8 mm	L-11
9 mm	M/N-13
10 mm	N/P-15
11.5 mm	P-16
12 mm	no US size listed
15 mm	P/Q
15.75 mm	Q
16 mm	Q
19 mm	S
25 mm	T/U/X
30 mm	T/X

Steel hooks are sized differently from regular hooks: the higher the number, the smaller the hook. The smallest steel hook is a #14 or 0.9 mm; the largest is a 00 or 2.7 mm (CYC). Hook letters and numbers differ between brands, so use the millimetre size. Source: Craft Yarn Council, Hooks & Needles, read 2026-10-02. Also see the knitting needle chart and yarn weight chart.

Frequently asked questions

What size is a G crochet hook in mm?

On the Craft Yarn Council chart, G-6 is 4 mm and a plain G is 4.25 mm. Brands differ slightly, so check the mm marked on the hook.

What mm is an H-8 crochet hook?

H-8 is 5 mm on the Craft Yarn Council chart. I-9 is 5.5 mm and 7 is 4.5 mm.

Why are some hook sizes blank in the US column?

The CYC chart lists no US letter for 2.5 mm, 7 mm and 12 mm hooks. Use the millimetre size.

Are steel crochet hooks the same as regular hooks?

No. Steel hooks are used with lace weight yarn and crochet thread, and their numbering runs backwards: a larger number is a smaller hook. The CYC gives the range as #14 (0.9 mm) to 00 (2.7 mm).