The standard international unit of measurement for paper weight, expressed in grams per square meter, or gsm. Grammages range from 7 to approx. 225 g/m2 for paper, and approx. 150 to 600 gsm for board. The system differs in the U.S., where the term basis weight is used, i.e. the weight in pounds of a ream (500 sheets) in the basic size for a grade of paper.