Caliper

A caliper is a precision measuring instrument designed to determine the physical thickness of a material. In the paper industry, a micrometer caliper is the standard tool for measuring sheet thickness, often expressed in microns or millimeters. This measurement is distinct from grammage (GSM), which indicates mass per unit area.

While GSM tells you how heavy a sheet is, the caliper reveals how thick it is. Different paper stocks with the same GSM can have different thicknesses depending on their density and fiber composition. For business cards, a paper caliper helps verify that the final stock meets the intended weight class, such as 300 GSM or 400 GSM, ensuring the card has the expected structural rigidity and tactile quality.

US paper suppliers often quote caliper in points (pt): 1 pt = 0.001 in = 0.0254 mm — an exact, direct conversion (1 pt = 25.4 µm). This is not the typographic point (1/72 in) used for type sizes. pt and GSM are not equivalent — pt is thickness and GSM is weight, related only through the stock’s density. The same GSM can be a different pt from one stock to another.