ASTM D 646 : 1996

1.1 This test method covers the determination of the grammage of paper and paperboard (mass per unit area). In English-speaking countries the customary or commercial practice of expressing the "weight" per unit area (more properly "mass per unit area") of paper has been "basis weight," "ream weight," or "substance," defined as the mass in pounds of a ream of a given sheet size and number of sheets (usually 500 sheets, occasionally 480 sheets). In most other countries and increasingly in English-speaking countries, the mass per unit area is expressed in grams per square metre. The French term for mass per unit area," grammage," is recommended by ISO Committee TC 6 on Paper for use in English as well as in French because of its convenience and clear relationship to grams per square metre.

1.2 The mass per unit area of paperboard has been expressed in the customary system as the mass in pounds per thousand square feet, and in the metric system as grams per square metre.

1.3 The SI metric units, in which grammage (mass per unit area) is expressed in grams per square metre (g/m²), are the preferred units for ASTM test methods for paper and paperboard.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.