In the U.S., the traditional method of determining paper weight is formally known as basis weight, and is the weight (in pounds) of a stack of 500 sheets of paper. This is where much of the confusion comes in, because different types of paper have different uncut sizes used as the basis of this weight.
It is important to note that paper thickness and paper weight are not the same thing. The type of paper affects how thick that sheet will be for any given basis weight. For instance, a sheet of 100 lb. offset cover is about 14 pt., or 0.0140 inches thick. However, 100 lb. gloss cover, which has the same basis weight, is closer to 9 pt. (o.0092 inches). As a result, the 14 pt. offset cover stock is quite a bit stiffer than the equivalent gloss cover stock.
If you know the outer diameter of the roll and the core on which paper is wound and the thickness of the paper and basis weight, you can calculate the weight of paper on roll using following equations.
A well beaten/refined pulp, short fiber pulp such as hard wood or straw pulp,highly filled or loaded paper will show lower thickness for given basis weight.
If you know the net weight (Total weight - Core weight) of the roll and the Basis weight of the paper, you can calculate the length of paper using following equations.
Breaking length is generally used in the paper trade to characterize the inherent strength of paper. It affords an excellent basis for comparing the strength of papers made from different furnishes and having different basis weight.