It is important to note, that not all crochet hooks or knitting needles are created equal. A 6mm hook or needle in one brand, may not be exactly the same size as a 6mm hook or needle in a different brand. This only one of the reasons why checking gauge is so important with your crochet and knit projects. When a pattern calls for a certain hook or needle size, this is a recommendation based on what the designer used personally and does not necessarily mean that you will achieve the same gauge with the same size hook or needles. Regardless of the number or marking on your hook or needle, always complete a gauge swatch and match it to the gauge of your pattern. If your swatch is larger than the pattern gauge, complete another swatch using a smaller hook or needle size. Alternately, if your swatch turns out too small, adjust to a larger hook or needle size in order to achieve the gauge required by the pattern.
For more information on gauge and why it is so important, check out this blog post.
Hook and needle sizes as well as materials can vary widely between suppliers. Below are conversion charts for and array of hook and needle sizes.
CROCHET HOOK SIZE CHART
Millimeter Range
US Size Range
2.25 mm
B-1
2.50 mm
2.75 mm
C-2
3.125 mm
D
3.25 mm
D-3
3.50 mm
E-4
3.75 mm
F-5
4 mm
G-6
4.25 mm
G
4.50 mm
7
5 mm
H-8
5.25 mm
I
5.50 mm
I-9
5.75 mm
J
6 mm
J-10
6.50 mm
K-10 ½
7 mm
8 mm
L-11
9 mm
M/N-13
10 mm
N/P-15
11.50 mm
P-16
12 mm
15 mm
P/Q
15.75 mm
Q
16 mm
Q
19 mm
S
25 mm
T/U/X
30 mm
T/X
KNITTING NEEDLE SIZE CHART
Millimeter Range
US Size Range
1.50 mm
000
1.75 mm
00
2 mm
0
2.25 mm
1
2.75 mm
2
3 mm
3.125 mm
3
3.25 mm
3
3.50 mm
4
3.75 mm
5
4 mm
6
4.25 mm
6
4.50 mm
7
5 mm
8
5.25 mm
9
5.50 mm
9
5.75 mm
10
6 mm
10
6.50 mm
10 ½
7 mm
8 mm
11
9 mm
13
10 mm
15
12.50 mm
17
12.75 mm
17
15 mm
19
19 mm
35
25 mm
50
35 mm
70