Knitting Needle Sizing Chart

Here's a helpful knitting needle size chart that breaks down the millimeter (mm) size vs. US number size (#). 

MM Needle Size US # Needle Size
 2mm #0
2.25mm
#1
2.75mm
#2
3.25mm #3
3.5mm #4
3.75mm #5
4mm #6
4.5mm #7
5mm #8
5.5mm #9
6mm #10
6.5mm #10.5
7mm #10.75
8mm #11
9mm #13
10mm #15
12mm #16
12.75mm #17
15mm #19
19mm #35
25mm #50