Jewelry Measurement Conversions and Charts

Download this Jewelry Measurements PDF  Download this Page for Easy Printing (132 KB)

Quick Jump: Cabochons | Beads | Wire | Jump Rings

Cabochons and beads are commonly measured in millimeters (mm), while many people in the United States are more familiar with inches (in). Here are some easy ways to figure out what size cabochon or bead to work with!

If you're looking for help with how many feet are in an ounce or pound of wire, click here!

  • To convert inches to mm, multiply inches by 25.4
  • To convert mm to inches, divide millimeters by 25.4


In most cabochon measurements, the height comes first, then the width (which may seem backwards).

Here are some common cabochon sizes, in millimeters and inches.

8 x 6mm Cab

8 x 6mm Cab

0.3" x 0.25" Cab

14 x 10mm Cab

14 x 10mm

0.6" x 0.4"

18 x 13mm Cab

18 x 13mm

0.7" x 0.5"

25 x 18mm Cab

25 x 18mm

1" x 0.7"

30 x 22mm Cab

30 x 22mm

1.2" x 0.7"

40 x 30mm Cab

40 x 30mm

1.6" x 1.2"

Remember, there are 10 millimeters in 1 centimeter, so a 40 x 30mm cab can also be measured as 4 x 3 centimeters. Most rulers in the U.S. have one side for inches, and one side for centimeters.

For comparison, a U.S. Quarter is 24.26mm in diameter (across); a quarter is nearly the same size as a 25mm round cabochon.


U.S. Quarter


25mm Round Cab

25mm Round


A U.S. Penny is 19mm in diameter, or 3/4" across. Here's a penny compared to an 18 x 13mm cab:


U.S. Penny (19mm)

18 x 13mm Cab

18 x 13mm


Do you want to know the number of beads in a strand? If you know the length of the strand and the size of the beads, you can estimate the number of beads in any strand. Note: this method may not work on beads of different sizes on the same strand.

  1. Take the strand measurement and convert it to millimeters.
    On wirejewelry, most of our strands are 16" long, or 406.4mm.

  2. Divide the strand measurement by the size of the bead.
    For example, we have a 6mm round bead.
    6mm Bead
    406.4 ÷ 6 = 67.7
There are about 67 beads in a strand of 16" 6mm beads. Each strand may vary slightly by a few beads in either direction.

Wire Gauges's jewelry wire is measured according to AWG standards. Not every wire is available in each shape and gauge; the boxes left blank in the chart below indicate that we do not usually stock that gauge in that shape. All wire begins round, so it is the most common shape.

Here is how each shape is measured: How to Measure Wire Shapes
As you can see, the standard diameter and gauge of half round wire is measured across the flat part of the wire.

Here's a chart with the AWG Gauge (the gauge you're used to seeing, like 22-gauge), how wide that wire is in inches, how wide it is in millimeters, and approximately how large that is. Use this chart to determine what wire to use with beads and more! Please note, this is not to-scale on a monitor. Please download this chart before printing it to ensure it prints to scale. Make sure in your Print dialog box that the document prints at 100%, and does not scale it to fit your paper size.

Click to Download your Wire Gauge Chart

Jump Rings

Inner Diameter (ID) & Outer Diameter (OD)

Jump rings are typically measured by their Inner Diameter, Outer diameter, and wire gauge. For example, if you made your own jump rings from 18-gauge wire around a 5mm dowel, the Inner Diameter is 5mm, the gauge is 18-gauge (or 1.02mm, found in the chart above). But what's the outer diameter?

Jump ring inner diameter and outer diameter diagram

Some patterns call for jump rings measured in OD, some in ID. If you know either the ID or the OD as well as the gauge, you can find your missing measurement.

To find the Inner Diameter (OD)

Inner Diameter = OD - (wire gauge * 2)

To find the Outer Diameter (OD)

Outer Diameter = ID + (wire gauge * 2)

So using the example of an 18-gauge jump ring made around a 5mm dowel, remembering that 18-gauge is 1.02 mm:

OD = 5 + (1.02*2)

OD = 5 + 2.04

OD = 7.04mm for an 18-gauge jump ring with a 5mm ID.

Download this Page as a Printable PDF

If you print directly from this page, the cabochon and wire gauge sizes may not print at the right size. Here's a downloadable PDF so you can print out the page perfectly to scale!

Download this Jewelry Measurements PDF  Download Jewelry Measurement Conversions and Charts (132 KB)  |  Download Adobe Reader