mm Inches Inches mm Inches Inches
1 0.04 1/32 inch   26 1.02 1 and 1/32 inch
2 0.08 1/16 inch    27 1.06 1 and 1/16 inch
3 0.12 3/32 inch   28 1.10 1 and 3/32 inch
4 0.16  1/8 inch   29 1.14 1 and 1/8 inch
5 0.20 3/16 inch   30 1.18 1 and  3/16 inch
6 0.24  Just under 1/4 inch   31 1.22  Just under 1 and 1/4 inch
7 0.28 Just over 1/4 inch   32 1.26 Just over 1 and 1/4 inch
8 0.31  5/16 inch   33 1.30  1 and 5/16 inch
9 0.35 Just under 3/8 inch   34 1.34 Just under 1 and 3/8 inch
10 0.39  Just over 3/8 inch   35 1.38  Just over 1 and 3/8 inch
11 0.43 7/16 inch   36 1.42 1 and 7/16 inch
12 0.47  Just under 1/2 inch   37 1.46  Just under 1 and 1/2 inch
13 0.51 Just over 1/2 inch   38 1.50 Just over 1 and 1/2 inch
14 0.55  9/16 inch   39 1.54  1 and 9/16 inch
15 0.59 Just under 5/8 inch   40 1.57 Just under 1 and 5/8 inch
16 0.63  5/8 inch   41 1.61  1 and 5/8 inch
17 0.67 Just under 11/16 inch   42 1.65 Just under 1 and 11/16 inch
18 0.71  Just over 3/4 inch   43 1.69  Just over 1 and 3/4 inch
19 0.75 Just over 3/5 inch   44 1.73 Just over 1 and 3/5 inch
20 0.79 Just under 13/16 inch   45 1.77 Just under 1 and 13/16 inch
21 0.83 Just over 13/16 inch   46 1.81 Just over 1and  13/16 inch
22 0.87  Just under 7/8 inch   47 1.85  Just under 1 and 7/8 inch
23 0.91 Just over 7/8 inch   48 1.89 Just over 1 and 7/8 inch
24 0.94  15/16 inch   49 1.93  1 and 15/16 inch
25 0.98 1 inch   50 1.97 2 inches

For comparison purposes, here are the Thickness measurements of some common US coins:

In order To get clearer understanding of how thick or wide is a piece of jewelry, you can use US coins for reference. For thicker items you can stack multiple coins to acquire the approximate thickness or the width of your selected jewelry.