Weight per a selected unit of area of a grade of paper; grammage or "grams per square meter" is used throughout the world and scientifically in the United States; the U.S. uses many different basis weight designations, depending upon the type of paper, including in fine paper, but not limited to: lbs. per 25" X 38"-500 sheets: text, book, offset lbs. per 17" X 22"-500 sheets: writing, bond, ledger lbs. per 20" X 26"-500 sheets: cover lbs. per 24" X 36"-500 sheets: newsprint, tag, tissue, board The 500 sheets represent the standard "ream" count, and is the basic unit for determining area. Also called substance weight, particularly in the bond or business grades of paper. The weight in pounds of a ream of paper, typically consisting of 500 sheets cut to its basic size.