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 jewellery 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 jewellery with double zeros being the largest size plugs generally available.
Find the thickest earring or plug that you can wear comfortably out of your jewellery.
Measure the thickness of the earring or plug with a caliper. Position the jewellery between the two arms of the caliper and move the bottom arm up until both arms are touching the jewellery. Note the size of the jewellery as the caliper displays it in millimetres.
Use a sizing chart, such as the one at the Organic Earrings website, convert millimetres to the proper gauge size for your piercing.