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 per square metre (g/m 2 ), 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 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 per square metre (g/m 2 ), 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/m 2 ). 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})} Typical office paper has , therefore a typical A4 sheet ( of a square metre) weighs . The abbreviation gsm instead of the standard g/m 2 symbol is also widely encountered in English-speaking countries. Typically grammage is measured in paper mill on-line by a quality control system and verified by laboratory measurement. ==Basis weight== Basis weight of paper is the density of paper expressed in terms of the mass (in pound) of a ream of paper of given dimensions and a sheet count. The American and the traditional British systems are largely the same, with only minor differences: the paper dimensions and the sheet count are different. ==Caliper== Paper thickness, or caliper, is a common measurement specified and required for certain printing applications. Since a paper's density is typically not directly known or specified, the thickness of any sheet of paper cannot be calculated by any method. Instead, it is measured and specified separately as its caliper. However, paper thickness for most typical business papers might be similar across comparable brands. If thickness is not specified for a paper in question, it must be either measured or guessed based on a comparable paper's specification. Caliper is usually measured in micrometres (μm), or in the United States also in mils (1 mil =  in = 25.4 μm). Commonly, 20-pound bond paper ranges between roughly in thickness. The paper density is calculated by dividing the grammage over the caliper, and is usually expressed in grams per cubic centimetre (g/cm 3 ) to cancel out the mathematical need for unit conversions between metres and micrometres (a conversion factor of 1,000,000). ==See also== Density Area density Linear density Envelope size Hole punch — filing holes Index card Paper and ink testing Photo print sizes ==Notes== ==References== ==External links== Understanding Paper Weights Understanding paper weight (Staples Inc.) M-weight Calculator Paper Weight Calculator Paper Weight Conversion GSM to LBS

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