1.1 This method describes a procedure for measuring the thickness of a single sheet of paper or paperboard using soft synthetic rubber platens against the paper to minimize the effect of surface roughness. This method is not to be confused with nor substituted for TAPPI T 411 Thickness (Caliper) of Paper and Paperboard and Combined Board. It is to be used primarily for sheet density calculations. Because of the relatively high pressure (50 kPa), this method may not be suitable for measurement of tissue or other soft or low density materials, because the structure may collapse at the prescribed pressure of 50 kPa (7.2 psi).

1.2 Other methods which yield similar results are the mercury displacement method and the effective thickness concept (2).

1.3 TAPPI T 411 Thickness (Caliper) of Paper, Paperboard, and Combined Board describes a method for measuring thickness using hard platens. This method is affected by surface roughness, and the measured thickness is always higher than that determined by the soft platen method.