Standard ear piercings are usually pierced at 20g or 18g. Gauge sizes go up (or down, depending on how you look at it) in even numbers from there, so the next largest size from an 18g is 16g, then 14g, then 12g, and so on. When you get to 0g, the next size is 00g (pronounced “double zero gauge"). 00g is equal to about 3/8 of an inch.