The etymology of grammage takes us to the French word grammage. The term refers to weight of the paper by square meter, Expressed in grams.
It is understood by paper to the thin sheet that is produced with the vegetable fiber pulp. The papers can be used for writing, drawing, printing or wrapping, to name a few possibilities.
Square meter, meanwhile, it is a unit of surface equivalent to the surface of a square whose sides measure one meter each. Gram, for its part, is a unit of mass that is equal to 0.001 kilograms.
With these ideas clear, we can understand what grammage is, a concept that is also known by the name of basis weight. If we have a surface of a square meter of paper, the grammage will be its weight in grams. It is, in short, a characteristic of the paper.
Many times the grammage is confused with the thickness (which is the distance between the two faces of a sheet). Both properties they are usually linked since, in general, the grammage increases as the thickness increases. However, it must be borne in mind that two papers with the same grammage may have different thicknesses and vice versa.
The paper of daily or newsprint usually has a grammage of about 42 g / m². This means that if we take a sheet of newsprint with an area of one square meter (a square with four sides of one meter), its weight will be 42 grams.
The difference in grammage between papers of different types is the reason why this concept must exist, since the industry The paper mill must invest money in the manufacture and distribution of the reams taking into account the number of sheets that can be processed and transported at one time, one of the factors that influence the decision of the sale price.
Let’s look at some types of paper with different weights: coated paper, also know as couché, and characterized by its texture satin has a variable weight, with a range that starts at 60 grams and ends at 350 grams per square meter; the offset paper it has the same grammage, although it is very porous and especially absorbent for ink; the creative paper it is very rigid, it is used in high resolution printing, and its weight ranges from 100 to 300 grams.
To calculate the grammage, you first need to weigh the paper in a balance. A simple rule of three can then be used to determine grammage. Let’s look at the example of a sheet of paper 50 square centimeters (c²) with a weight of 30 grams:
50 square centimeters = 0.5 square meters
0.5 square meters = 30 grams
1 square meter = x grams
(1 square meter x 30 grams) / 0.5 square meters = 60 g / m²
The weight of the sheet in question, therefore, is 60 g / m².
Within this framework, it is important to clarify the way in which certain countries calculate and express the weight of materials related to this concept, which in addition to paper include the cloth, for instance. As indicated in the previous paragraphs, grammage refers to the value in grams per square meter of a given material. However, it is also possible to measure the mass based on the number of leaves, to give rise to the aforementioned basis weight.
Basis weight is convention used in North America and other countries, where it is expressed in pounds per ream of 500 or 1000 sheets that have not yet been cut into a specific format. In Japan, on the other hand, it is stated as the weight in kilograms of reams of a thousand sheets. There are also places where both concepts, grammage and basis weight, are used together.