The most important gauge on belly button rings is the piercing gauge itself; the belly button ring gauge, which indicates the size of the actual piercing within your navel.
14G is the standard belly button ring gauge size.
16G a slightly thinner gauge, is one of the belly ring sizes most often thought of as the other navel ring size.
When shopping for a belly button ring, remember to look over Piercing Size Chart to make sure you understand what the measurements actually mean.
All of these body jewelry measurements, and specifically, all of these belly button ring sizes, are going to help you determine which belly ring is going to fit and look the best on you.