Grammage

Basis weight and grammage are terms used in the pulp and paper industry and also for fabric industry to denote a measure of mass of the product per unit of area for a type of fabric, paper or paperboard. Two ways of expressing grammage are commonly used:

In the metric system, the mass per unit area of all types of paper and paperboard is expressed in terms of grams per square meter (g/m²). This quantity is commonly called in both English and French (ISO 536), though printers in most English-speaking countries still refer to the "weight" of paper.

Typical office paper has 80 g/m², therefore a typical A4 sheet ( ¹⁄₁₆ m²) weighs 5 g. The unofficial unit symbol "gsm" instead of the standard "g/m²" is also widely encountered in English speaking countries.

Typically grammage is measured in paper mill on-line by Quality Control System (QCS) and verified by laboratory measurement.

In countries that use US paper sizes, a less direct measure known as basis weight is used in addition to or instead of grammage. The basis weight of paper is the density of paper expressed in terms of the mass of a ream of given dimensions and a sheet count. In the US system, the weight is specified in avoirdupois pounds and the sheet count of a paper ream is usually 500 sheets. However, the mass specified is not the mass of the ream that is sold to the customer. Instead, it is the mass of the uncut "basis ream" in which the sheets have some larger size. Often, this is a size used during the manufacturing process before the paper was cut to the dimensions in which it is sold. So, to compute the mass per area, one must know

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