The thickness of paper is often measured by caliper, which is typically given in thousandths of an inch in the United States and in thousandths of a mm in the rest of the world. Paper may be between 0.07 and 0.18 millimetres (0.0028 and 0.0071 in) thick.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): What tool is often used in measuring the thickness of paper?
caliper