From Manfred Breede:
Basis Weight is the weight in pounds of 500 sheets of a basic size in inches that varies with a given paper category. In the US, and also in Canada, Basis Weight is the predominant method to quantify the weight of paper. In most other countries the weight of paper is based on the weight in grams of a single sheet of paper having an area of 1 square meter. This method is called Grammage. The BasisWeight5 app converts the Grammages of 8 paper categories to Basis Weights with an absolute minimum of user input. There is no need for the user to know the basic size of a given paper category, let alone entering it. To display conversions from Grammage to Basis Weight values, the BasisWeight5 app requires nothing more than entering the Grammage of a paper into a Text Field, followed by clicking one of 8 Buttons, each one of which represents a different paper category.