Hi. Below is a size conversion chart to help to determine jewelry bead sizes.

1mm = 1/32"
2mm = 1/16" 
3mm  = 3/32"
4mm  = 1/8"
5mm  = 3/16"
6mm  = Just under 1/4"
7mm  = Just over 1/4"
8mm  = 5/16"
9mm  = Just under 3/8"
10mm   = Just over 3/8"
11mm  = 7/16"
12mm  = Just under 1/2"
13mm  = Just over 1/2"
14mm  = 9/16"
15mm  = Just under 5/8"
16mm  = 5/8"
17mm  = Just under 11/16"
18mm  = Just over 3/4"
19mm  = Just over 3/5"
20mm  = Just under 13/16"
21mm  = Just over 13/16"
22mm  = Just under 7/8"
23mm  = Just over 7/8"
24mm  = 15/16"
25mm  = 1"

Enjoy!