In many of the world, sheet steel thickness is constantly specified in millimeters. In the united states, the thickness of sheet steel is often specified by a traditional, non-linear measure identified as|often recognized as} its gauge. Commonly used steel sheet steel ranges from 30 gauge to stylus pen for note 5 about 7 gauge. Gauge differs between ferrous (iron-based) metals and nonferrous metals similar to aluminum or copper. Copper thickness, for instance, is measured in ounces, representing the weight of copper contained in an area of 1 sq. foot.