Weight of Sheet Steel
The following table provides sheet steel thicknesses and weights in both US and metric according to the Manufacturers’ Standard Gauge for Sheet Steel (MSG), which is the primary commercial gauge system used by sheet steel manufacturers in the United States today. When you buy sheet steel, these are typically the weights and thicknesses you’ll be getting, although actual finished products may vary slightly according to industry-accepted manufacturing tolerances (small variations from the standard due to practicality in the manufacturing process). These tolerances go from around (+-) 4.5% for 10 gauge steel to around 8.5% for 15 gauge steel and higher. (If these were rocket ship parts, the tolerances would be much, much smaller.) A full table of ASTM-AISI standard sheet steel tolerances by gauge number can be seen here.
For a look at the old legal “Standard Gauge for Sheet and Plate Iron and Steel”, which is not generally used commercially any more, see this page at the Cornell Law School website.
The Manufacturers' Standard Gauge for Sheet Steel assumes an average density for carbon steel of 41.82 lb per square foot per inch thick, and the standards for each gauge number are derived from that.
Galvanized steel is formed by applying a very thin coating of zinc to a steel sheet. Approximately the same amount of zinc is applied regardless of the gauge of the steel, so the thickness and weight of galvanized steel by gauge can be determined by adding a constant to the values for the plain steel gauges (see the table below).
Corrugated steel, which is used for roof decks and some roof and wall panels, will weigh from 30% to 70% more per square foot as a finished product than flat sheet steel of the same gauge due to the corrugation. The precise increase in weight depends on the depth and spacing of the ribs, which varies from product to product. The weight per square foot should be available on the website of the manufacturer.
The values provided in the table are standards; real-life products will vary. These values should not be used if extreme precision is needed for critical engineering calculations. When such precision is required, always refer to the data sheets of the actual, specific product you intend to use, or better yet, contact the technical department of the product manufacturer.
Manufacturer technical data sheets (with the material weights and thicknesses) are almost always made available on the websites of reputable manufacturers.