Standard steel gauges range from gauge 3, which is 6.07 millimeters in thickness, to gauge 38, which is 0.015 millimeters in thickness. Engineering websites, including EngineersEdge.com, EngineersHandbook.com and SIMetric.co.uk provide online sheet steel gauges. These charts provide information about the standard weight and thickness of metal at particular reference points.
As the gauge number increases, the theoretical thickness of the steel decreases. However, charts only indicate the ideal thickness at any standard gauge; in reality, manufacturing variations mean that the thickness of a given piece of metal may vary quite significantly from the published numbers. Processing, such as polishing, etching or working, can also alter the sheet thickness and make chart figures less accurate. Any additional protective coatings also alter the gauge.