Grammage is specified in avoirdupois pounds and the sheet count of a paper ream is usually 500 sheets. However, the mass specified is not the mass of the ream that is sold to the customer. Instead, it is the mass of the uncut "basis ream" in which the sheets have some larger size (parent size). Often, this is a size used during the manufacturing process before the paper was cut to the dimensions in which it is sold. So, to compute the mass per area, one must know The standard dimensions and sheet count of a ream vary according to the
Paper size the sheet of paper is folded in half widthwise, let "c" be the length of the new short side: "c" = . If we take the ratio of the newly folded paper we have: formula_3 Therefore, the aspect ratio is preserved for the new dimensions of the folded paper. Weights are easy to calculate as well: a standard A4 sheet made from 80 g/m paper weighs 5 g (as it is of an A0 page, measuring 1 m), allowing one to easily compute the weight—and associated postage rate—by counting the number of sheets used. The advantages of basing a paper