Ten-gauge steel is 0.1345 inch thick. This refers to normal steel, as the numbers change for galvanized steel, stainless steel, and sheet and plate steel.
Ten-gauge galvanized steel is 0.1382 inch thick, and 10-gauge stainless steel is 0.1406 inch thick. The values differ because gauge is a measurement of weight, not thickness. The Manufacturers' Standard Gauge for Sheet Steel is based on an average weight of 41.82 pounds per square foot per inch thick. Gauge and thickness are inversely related; the higher the gauge number, the thinner the steel. Other metals, such as aluminum and zinc, use different gauge measurements.