If you have ever purchased or shopped for a piece of jewelry online or in a catalog, perhaps you have noticed that most companies measure the size of their jewelry in millimeters, not inches. For many U.S. buyers who do not use the metric system on a daily basis, this causes difficulty in being able to accurately gauge the size of a piece of jewelry in their mind, and can result in disappointment if the piece is much larger or smaller than they imagined.

However, the following chart will help you to accurately determine how large a piece of jewelry or a gemstone truly is, so you will better understand the dimensions of the piece you are looking to purchase:

1 mm = approximately 1/32" 21 mm = approximately 13/16"
2 mm = approximately 1/8" 22 mm = approximately 7/8"
3 mm = approximately 1/8" 23 mm = approximately 15/16"
4 mm = approximately 3/16" 24 mm = approximately 15/16"
5 mm = approximately 3/16" 25 mm = approximately 1"
6 mm = approximately 1/4" 26 mm = approximately 1"
7 mm = approximately 1/4" 27 mm = approximately 1 1/16"
8 mm = approximately 5/16" 28 mm = approximately 1 1/4"
9 mm = approximately 3/8" 29 mm = approximately 1 1/8"
10 mm = approximately 3/8" 30 mm = approximately 1 3/16"
11 mm = approximately 7/16" 31 mm = approximately 1 1/4"
12 mm = approximately 1/2" 32 mm = approximately 1 1/4"
13 mm = approximately 1/2" 33 mm = approximately 1 5/16"
14 mm = approximately 9/16" 34 mm = approximately 1 3/8"
15 mm = approximately 5/8" 35 mm = approximately 1 3/8"
16 mm = approximately 5/8" 36 mm = approximately 1 7/16"
17 mm = approximately 11/16" 37 mm = approximately 1 1/2"
18 mm = approximately 3/4" 38 mm = approximately 1 1/2"
19 mm = approximately 3/4" 39 mm = approximately 1 9/16"
20 mm = approximately 13/16" 40 mm = approximately 1 9/16"


In word to remeber is this every 25 MM's equals 1-inch and 12.5 MM equals 1/2-inch and so on.

For comparison purposes, here are the diameter measurements of some common items:


Dime = 17mm
Penny = 19mm
Nickel = 21mm
Quarter = 24mm


It is also important to make sure that you understand the definition of what the specific measurement is for. Here are some commonly misunderstood definitions:

Diameter: The distance of a straight line segment passing through the center of a figure, especially of a circle or sphere, and terminating at the edges
Circumference: The size of an item as given by the distance around it.

We do hope this information helps you to make a more informed purchase; we always welcome any questions or suggestions regarding this guide or any of our items. Happy Jewelryshopping!