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Grammage and Basis Weight

Do you know the differences between Grammage and Basis Weight?

What is the meaning of grammage and basis weight?

Today we will share you the definition of them. Let us know more about paper.

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:

  • Expressed in grams per square meter (g/m2), paper density is also known as grammage.This is the measure used in most parts of the world.

  • Expressed in terms of the mass (expressed as weight) per number of sheets, it is known as basis weight. The convention used in the United States and a few other countries using US paper sizes is pounds of a ream of 500 (or in some cases 1000) sheets of a given (raw, still uncut) basis size. Japanese paper is expressed as the weight in kg of 1,000 sheets.

1. 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 meter (g/m2). This quantity is commonly called grammage 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 ( 116 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.

2. Basis weight

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:

  • the mass of the basis ream,

  • the number of sheets in that ream, and

  • the dimensions of an "uncut" sheet in that ream.

The standard dimensions and sheet count of a ream vary according to the type of paper. These "uncut" basis sizes are not normally labelled on the product, are not formally standardized, and therefore have to be guessed or inferred somehow from trading practice. Historically, this convention is the product of pragmatic considerations such as the size of a sheet mold.

(The above is from Wikipedia.)

Now, could you distinguish grammage and basis weight?

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