Crochet hook sizes: millimeters, letters and numbers

By Kimberly from Skeinstead · Updated Oct 22, 2026

US crochet hooks are labeled with a letter, a number, or both, plus a size in millimeters. The Craft Yarn Council points out that letter and number sizing varies between companies, and recommends relying on the millimeter size, which is an exact measurement.

Common hook sizes

Selected sizes from the Craft Yarn Council hook chart
Metric	US letter/number
2.25 mm	B-1
2.75 mm	C-2
3.25 mm	D-3
3.5 mm	E-4
3.75 mm	F-5
4 mm	G-6
4.5 mm	7
5 mm	H-8
5.5 mm	I-9
6 mm	J-10
6.5 mm	K-10½
8 mm	L-11
9 mm	M/N-13
10 mm	N/P-15
11.5 mm	P-16
15 mm	P/Q
16 mm	Q
19 mm	S

Steel hooks are different

Steel hooks, used for thread crochet, are numbered the other way around: the higher the number, the smaller the hook.

Picking the right hook

Start with the hook on your pattern, or on your yarn label if the pattern doesn't say.
Make a gauge swatch.
Too many stitches per 4 in? Go up a hook size. Too few? Go down.

Kimberly's tip: When you write down a project, write the hook in mm. "H" means 5 mm almost everywhere in the US, but "5 mm" is never ambiguous.

Sources

Craft Yarn Council: Hooks & Needles (checked Oct 22, 2026)