This method describes the procedure for measuring single-sheet thickness and variations in single sheet thickness of paper, paperboard, and combined board. The term combined board encompasses both corrugated and solid fiberboard.
Selection of samples/specimens cut across the web (perpendicular to the machine direction) may be used to determine the cross machine caliper profile.
Because of the relatively high pressure 50 kPa (7.3 psi) used in this test method, it may not be suitable for measurement of tissue or other soft or low density materials, because the structure may collapse (decrease in thickness) at the prescribed pressure of 50 kPa. TAPPI T 580 Thickness (caliper) of towel, tissue, napkin and facial products should be used to measure these products. It uses a lower pressure of 2 kPa and a larger movable face with an area of 10 cm2.
Another method for measuring the thickness of paper is TAPPI T 500 Book Bulk and Bulking Number of Paper, which describes a procedure for measuring the overall thickness of a stack of book paper under pressure of 250 kPa (35 psi).
An essentially identical method is described in ASTM D 645-96.
TAPPI T 551 Thickness of Paper and Paperboard (Soft Platen Method) describes a method for measuring the effective thickness of paper and board products utilizing soft rubber platens. This method always yields smaller values than TAPPI T 411.