The gauge(or sometimes just the number listed) of piercings is a measurement of the thickness of the wire used for the piece. Using the system is easy, if not immediately intuitive. What you need to know is:
Wire gauge gets higher as the wire thickness gets smaller
For example 16 gauge = 1.29mm diameter 18 gauge = 1.02mm diameter 20 gauge = 0.813mm diameter 22 gauge = 0.643mm diameter In other words, the thinner the wire is, the higher the gauge will be. Or, the thicker the wire is, the lower the gauge will be.
Wire gauge can be measured using two different systems
American Wire Gauge (AWG) and Standard Wire Gauge(SWG) are the two different standards for measuring wire thickness AWG is used exclusively in my store as it is the industry standard for piercings in the US. SWG is common in chainmaille instructions and used in Canada as well as some other formerly British countries. It is VERY rare to see SWG used in referance to piercings, but it is good to know and be aware of the difference.
The most common wire gauges for jewelry & chainmaille are between 14 gauge and 22 gauge
My father(of UnkamenSupplies) lives in chainmaille world, and I do too, a little. Chainmaille most commonly uses 16, 18, or 20 gauge wire. 22 gauge and higher are often used for wire wrapping. Gauges smaller than 14 (remember, smaller means thicker) are commonly used for applications where strength is more important than fine details.
In the world of piercings, body jewelry gauges usually range from 22 to 00g – after 00g, jewelry then goes to actual measurements such as with 1/2 inch plugs. 20 gauge is the industry standard for traditional earlobe piercings. This is the gauge they use at most mall stores and is what nearly all standard earrings use. Some people with very sensitive ears, or earrings made with solid gold, may use 22 gauge for their earrings. Most standard lobe piercings will also fit 18 gauge, though it may feel “snug” at first.
Cartilage piercings usually are 16 gauge or 14 gauge, depending on the piercing studio, or the exact location of the piercing.14 gauge is most often used for most other body piercings such as in the eyebrow, navel, or tongue.