The gauge size for a septum piercing can vary depending on the individuals anatomy and the piercers discretion. However, generally speaking, the standard gauge size for a septum piercing is 16 gauge (1.2 mm) . It is also available in 18 gauge (1 mm) . Some people may choose to size down to 18 gauge or size up to 14 gauge depending on their specific needs. It is important to know the gauge size of your septum piercing to avoid damaging the piercing or accidentally downsizing it when purchasing new jewelry. If you dont remember the gauge size of your septum piercing, it is recommended to ask your piercer prior to buying any new jewelry.