Steel crochet hooks are generally used with crochet threads and lace-weight yarns. They are sized differently than regular hooks: the higher the number, the smaller the hook, which is the reverse of regular hook sizing. Crochet thread is similarly sized: the smaller the number, the thicker the thread.

As with regular crochet hooks, there are variations in steel crochet hooks numbering. Regardless of the number or millimeter sizing, always complete a gauge swatch and compare it to the pattern gauge information.

The most common crochet threads are sizes 3, 5, 10, 20, and 30, though they are available in increments of 10 up to size 100, which is the finest.

Crochet Hook Sizes

Millimeter Range	U.S. Size Range
3.50 mm	00
3.25 mm	0
2.75 mm	1
2.70 mm	00
2.55 mm	0
2.35 mm	1
2.25 mm	2
2.20 mm	2
2.10 mm	3
2 mm	4
1.90 mm	5
1.80 mm	6
1.75 mm	4/0
1.70 mm	5
1.65 mm	7
1.60 mm	6
1.50 mm	8/7/2
1.40 mm	9/8
1.30 mm	10
1.25 mm	9/4
1.15 mm	10
1.10 mm	11
1.05 mm	11
1 mm	12/6
0.95 mm	13
0.90 mm	14/8
0.85 mm	13
0.75 mm	14/10
0.60 mm	12