A normal ear piercing is performed with an 18-gauge needle and post. Making that hole larger by stretching or dermal punching will allow you to use larger gauge ear rings or plugs. Finding the correct size jewelry for your ear will ensure your earrings or plugs are comfortable to wear and will not irritate you. A lower gauge number actually means a larger piece of jewelry with double zeros being the largest size plugs generally available.
Find the thickest earring or plug that you can wear comfortably out of your jewelry.
Measure the thickness of the earring or plug with a caliper. Position the jewelry between the two arms of the caliper and move the bottom arm up until both arms are touching the jewelry. Note the size of the jewelry as the caliper displays it in millimeters.
Use a sizing chart, such as the one at the Organic Earrings website, convert millimeters to the proper gauge size for your piercing.