The density—or weight per unit volume—of a sheet of paper. It can be calculated either by dividing the basis weight by the caliper (or thickness) of a single sheet, or by dividing the grammage by the single-sheet thickness. Since basis weight varies according to the basic size of the ream of paper used, comparisons of apparent densities should be converted to a common basic size. In the metric system, apparent density is measured in grams per cubic centimeter.
A paper's apparent density is the result of all the myriad aspects of the papermaking process, from the consistency of the papermaking furnish to the degree of calendering, and affects nearly all the properties of paper. (See Paper and Papermaking: Paper Properties.)