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 containing less than 10 micrometers of paper The international paper size standard is ISO 216. It is based on the German DIN 476 standard for paper sizes. ISO paper sizes are all based on a single aspect ratio of the square root of 2, or approximately 1:1.4142. There are different series, as well as several extensions. The following international paper sizes are included in Cascading Style Sheets (CSS): "A3", "A4", "A5", "B4", "B5". The base A0 size of paper is defined as having an area of 1 m and a dimension ratio of 1 to , making the A0 paper