'100...weights and densities of paper'

A paper is weighed in two ways: measured in grammage or in terms of mass. Grammage is used in determining density of all types of paper and paperboard. It is expressed in form of grams per square meter (gsm). The term grammage is also referred to as “weight” of paper in most English countries. To define this kind of measurement, one square meter is one A0 size sheet or 16 A4 size sheets. It is important to know that different paper types have different basic sizes. For instance a 20 pound bond paper is equivalent to 75.3gsm while a 20 pound Bristol paper is equivalent to 43.9 gsm.

On the other hand, when a paper is measured in terms of mass (pounds) of a ream of given dimensions a particular number of sheets; it is referred to as the basis weight or paper density. In the United States, it is expressed in terms of avoirdupois pounds and sheet count is usually 500 sheets in one ream. But the mass of the ream is based on its uncut raw size or the original size before manufacturing process took place. To determine the mass per area, it is important to identify: the mass of the ream basis, the number of sheets in that ream and uncut sheet dimensions in that ream.

Standard dimension and sheet count differs according to paper type and paper weight is sometimes presented by the symbol”#”. For instance “20#” is 20 pounds per ream of 500 sheets.

the link below is a website with lots of helpful information on uses, types and variations of paper weights and sizes.

http://www.paper-crafts.org/weights.htm

typical wikipedia entry about paper weights and density all helps to start there and it does provide some useful terminology.

http://en.wikipedia.org/wiki/Paper_density