There is no such shotgun gauge.
12 gauge is thicker than 20 gauge. The lower the gauge, the thicker the sheet metal or wire.
20 gauge is thicker (the lower the number, the thicker the steel).
8.8 is thicker
10 GA vinyl is thicker than 6GA vinyl. The higher the gauge the thicker the vinyl.
The larger the gauge, the smaller the diameter. That makes 22 gauge wire not as thick as 18 gauge wire.