Introduction to Crochet: Crochet Hook Size Equivalencies

Here is a chart for determining hook size equivalencies between the letter, US number, and millimeter sizes.  However, not everything is standard all the time.  For example, you might find a G hook that is 4.25 mm and another that measures 4.0 mm.  Q hooks can vary anywhere from 15 to 16 mm with many being 15.75 mm.  There are also hooks that fall in between the letter sizes.  And just to add in one more wrinkle, remember that depending on your tension, you might want to go up or down a hook size or two so make sure that your finished product will match the pattern's listed size.

Letter	Number	Millimeters
B	1	2.25
C	2	2.75
D	3	3.25
E	4	3.5
F	5	3.75
G	6	4.25
H	8	5
I	9	5.5
J	10	6
K	10.5	6.5
L	11	8
M	13	9
N	15	10
P	16	11.5
Q	19	15.75

If you're ever unsure of a hook's size, here's a handy tool to use to check.  It works for crochet hooks and knitting needles, too!