The thickness of a piece of paper depends on the type of paper and the intended use. Thickness is measured in calipers, which are expressed in thousandths of an inch, according to Case Paper.
Case Paper features a handy, downloadable caliper chart for a single sheet of paper based on its grade and weight. For example, the bond paper sold in stores for general use has a basis weight of 20. For a 17 by 22 inch sheet, the caliper thickness is .004. Before packaging, the sheets are divided into two 8.5 by 11 inch sheets, each with a caliper thickness of .002.