Grammage

Grammage and basis weight, in the pulp and paper industry, are the area density of a paper product, that is, its mass per unit of area. Two ways of expressing grammage are commonly used:

• Expressed in grams (g) per square metre (g/m²), regardless of its thickness (caliper).^[1] 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 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 kilograms (kg) per 1,000 sheets.