There are two terms commonly used to describe paper weight:
• Basis Weight The basis weight of a paper is based on the weight of 500 sheets, measured in pounds, in that paper's basic sheet size. Note that the "basic sheet size" is not the same for all types of paper which makes comparisons of weight between different papers difficult.
• Caliper Caliper refers to the thickness of a sheet of paper measured with a micrometer and expressed in thousandth of an inch. Paper caliper should not vary more than +/- 5% to 7% within a sheet. Generally, there is a relation between caliper and basis weight in that the greater the caliper (the thicker the paper), the greater the paper weight. But not always.