The University of North Carolina at Chapel Hill says that standard 11 gauge steel is 0.1196 inches thick and galvanised 11 gauge steel is 0.1233 inches thick. The “How Many?” page has a full list of steel gauges and how thick they are. The UNC has put online “A Dictionary of Units of Measurement” by Russ Rowlett.
The “gauge” of metal is a way to measure how thick a piece of sheet metal is. If the gauge number of a metal is high, it means that it is thinner than metals with lower gauge numbers. Most sheet metal has a gauge somewhere between 30 and 7. According to Cornell, galvanised 11 gauge sheet metal is usually said to be about 1/8 of an inch thick, which is what the United States Code says.