The model is wearing the 8mm 14g option, but the right size for you depends on your anatomy and on how your piercing was placed. The best way to find the right length is standing up and measuring the distance between the hole of your piercing and the upper rim of your belly button in millimeters (mm). If the distance is 7.5mm, for example, then go with the 8mm option.
As for the thickness, the standard size for belly rings is 14 gauge (14g), which equals around 1.5mm, or 1/16 inch. If you haven’t been wearing jewelry in your piercing for some time, or the jewelry you are
currently wearing appears to be thinner than 14g, then go with 16g. 16g is slightly thinner than 14g (16g is about 1.2mm).
If you still have doubts or you don’t have a ruler with a millimeter scale, you can always send us a picture of your piercing with a ruler next to it. We are more than happy to help you.