If all this fractions of an inch, millimeter and gauge sh*t has you confused, have no fear and read on … Basically, all you need to remember is that gauge refers to the thickness of the body jewelry and length refers to the internal diameter (for rings) or length (for barbells). Other important tips include knowing that:
Diameters listed are internal diameters meaning they are measured on the inside of the ring or from the inside of each ball on a barbell.
The lower the gauge number, the thicker the body jewelry (i.e. 6ga is thicker than 8ga, and 0 gauge is thicker than 2 gauge).
If you convert the denominator (the bottom number) to 16 in all fractions of an inch, the numerator (the top number) will help you order all the sizes (or see this conversion chart or this pdf size chart).
And for those who don't give a phuck about math, we've created an easy-to-use pdf chart to figure out which size and gauge is best for you.