grammage

Grammage and basis weight, in the pulp and paper industry, are measures of the area density of a paper product, that is, its mass per unit of area. Two common ways of expressing the area density of a paper product are used: Expressed in grams (g) per square metre (g/m2), regardless of its thickness (caliper) (known as grammage). This is the measure used in most parts of the world. It is often notated as gsm on paper product labels and spec sheets. Expressed in terms of the mass per number of sheets of a specific paper size (known as basis weight). The convention used in the United States and a few other countries using US-standard paper sizes is pounds (lb) per ream of 500 (or in some cases 1000) sheets of a given (raw, still uncut) basis size. The traditional British practice is pounds per ream of 480, 500, 504, or 516 sheets of a given basis size. Japanese paper is expressed as the weight in kilograms (kg) per 1,000 sheets.

==Grammage== In the metric system, the mass per unit area of all types of paper and paperboard is expressed in terms of grams per square metre (g/m2). This quantity is commonly called grammage in both English and French, though printers in most English-speaking countries still refer to the "weight" of paper. \text{Grammage} = \frac{\text{mass} \text{ (g)}}{\text{length} \text{ }(\text{m}) \times \text{width} \text{ } (\text{m})}