How are paper weight thickness and density measured?

In the context of papermaking, the weight, thickness, and density of paper are measured using standardized methods to ensure consistency in quality and application.12

Basis Weight

Basis weight refers to the weight or substance per unit area of paper. Because paper properties are sensitive to moisture, samples must be brought to equilibrium under standard conditions (24° C or 75° F at 50 percent relative humidity) before testing. The measurement is typically based on a ream, which is now commonly defined as 500 sheets.12

Caliper (Thickness)

The thickness of paper is measured as caliper. This is determined by placing a single sheet of paper between two circular, parallel plane surfaces. The measurement is taken under a steady, standardized pressure ranging from 0.49 to 0.63 kilograms per square centimetre (seven to nine pounds per square inch).12

Density

Density, or specific gravity, is not measured directly but is calculated using the values obtained from the basis weight and the caliper. Paper density can vary significantly depending on the type of paper, ranging from approximately 0.1 gram per cubic centimetre for light packaging materials to 1.4 grams per cubic centimetre for dense papers like glassine.2