Paper

Paper varies in thickness and weight. Both measurements are used to calibrate stock. At the paper mill, the thickness of a sheet is measured in thousands of an inch (mils). For the purposes of bookmaking, this number is converted into pages per inch. Book papers may vary from 200 to nearly 1,000 pages per inch, but the commonly used 50-lb (23-kg) machine-finished papers generally run about 500-550 pages per inch, each leaf counting as two pages. That corresponds to an average thickness of about 0.004 in (4 mm) for the thickness of one sheet of 50 lb (23 kg) machine-finished paper.

Paper is sold by weight. Different grades of the same type of paper are distinguished by the weight of some standard quantity of that paper. For most of the world, the standard quantity is one sheet of paper per one square meter in area. In the United States, the system of basis weights is used to compare the weights of papers. The standard quantity is one ream, or 500 sheets, but the standard sheet size varies from one category of paper to another. For book papers, the standard sheet measures 25 x 38 in (64 x 97 cm). For cover stocks, the standard size is only 20 x 26 in (51 x 66 cm), so a 50 lb (23 kg) cover paper is nearly twice as heavy as a 50 lb (23 kg) book paper. For bond papers, the standard size is 17 x 22 in (43 x 56 cm), so a 20 lb (9 kg) bond is approximately equal to a 50 lb (23 kg) book paper.

In Europe, the metric A series of stock sizes is based on a standard sheet of paper, rectangular in shape (841 mm x 1189 mm) and one meter in area. This is called size A0. Cutting this sheet in half produces size A1; cutting the A1 sheet in half produces size A2, and so on down to size A5, which is 1/32 the area of A0. In this sizing system, all of the sheets have the same shape: the ratio of the short side to the long side is identical throughout the series of sizes.