Grammage is one of the parameters most frequently encountered in paper specifications. For very thin papers such as rolling paper, grammage is a fundamental value that affects both how the paper behaves on production lines and the dimensional and physical consistency of the final product. In this article, we look at the definition of grammage, how it is measured and why it is decisive in corporate paper selection, within a technical framework. We also summarise the technical definitions of bleached and unbleached paper, two terms that are often confused.
What is grammage?
Grammage is the mass of paper per unit area and is expressed in grams per square metre (g/m²). For example, a one-square-metre piece cut from paper with a grammage of 12 g/m² has a mass of 12 grams. Grammage does not directly express the thickness of the paper; two papers of the same grammage can have different thicknesses depending on their fibre structure and production conditions.
A short calculation example
A simple calculation shows what grammage means at product level. The area of a leaf measuring 108 × 44 mm is 0.108 m × 0.044 m = 0.004752 m². At 12 g/m², the mass of this leaf is approximately 0.057 grams, or about 57 milligrams. At such low values, even small deviations in grammage can produce proportionally significant differences.
How is grammage measured?
ISO 536 is used as the international reference for determining the grammage of paper and board. Because paper is a hygroscopic material, samples must be conditioned in a standard atmosphere before measurement (under ISO 187, typically 23 °C and 50% relative humidity). The general measurement steps can be summarised as follows:
- Taking samples from different areas (across the width and along the length of the reel)
- Conditioning the samples in a standard atmosphere
- Cutting pieces of precisely known area
- Weighing the pieces on a precision balance
- Dividing the mass by the area to calculate the g/m² value and averaging the results
In technical specifications, grammage is usually defined not as a single number but as a target value together with an acceptable tolerance range. Measurement results are compared against this range to assess whether the raw material or production batch conforms to the specification. Stating in the specification which standard and which conditioning conditions the measurement follows also ensures that results from different laboratories are comparable.
The relationship between grammage, thickness and density
Grammage alone does not define all the physical properties of paper. Thickness is measured separately in micrometres (µm), and the ratio of grammage to thickness gives the density of the paper. At the same grammage, a thicker paper has a lower density and a thinner paper a higher density. For this reason, technical specifications define grammage together with other physical parameters such as thickness where necessary.
Why does grammage matter in paper selection?
From a corporate and industrial perspective, the importance of grammage can be grouped under a few headings:
- Line performance: On interleaving lines, paper is processed from the reel in a continuous flow. Fluctuations in grammage can affect web tension as well as slitting and folding behaviour.
- Cutting and dimensional consistency: In Flat Booklet production, stack height and cut quality are linked to the consistency of the paper’s grammage and thickness.
- Booklet and pack size: With a fixed leaf count, changes in grammage and thickness affect booklet thickness and, in turn, the fit of the cover and packaging.
- Conformity with the specification: Grammage is a measurable and verifiable acceptance criterion in technical specifications shared with partners.
Consistency: distribution matters as much as the average
It is not enough for the average grammage of a paper to equal the target value. How evenly the grammage is distributed in the machine direction and cross direction, and how stable it remains from batch to batch, are also assessed. For this reason, checks carried out at raw material acceptance and during production are designed to monitor variability as well as the average value.
Bleached and unbleached paper: technical definitions
Paper types are often referred to by their colour, but the technical meaning of this distinction is whether or not the pulp has undergone a bleaching process during production:
- Bleached paper: Paper whose pulp has been through a bleaching process to remove or convert colour-giving components, resulting in a white appearance. In the NOVEX product range, this type is called Classic White.
- Unbleached paper: Paper whose pulp has not been bleached, so the fibres retain their natural colour tone, giving a brownish appearance. In the NOVEX product range, this type is called Organic Brown.
Both paper types are evaluated in grammages starting from 12 g/m²; requests for other grammages can be reviewed separately.
The terms bleached and unbleached describe only the type of treatment applied to the paper during production. Product type names are used to distinguish the paper’s colour and treatment type; they do not imply any health or environmental attribute.
For more information on paper types and standard grammage values, see the Products and Quality & Compliance pages.
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