Definitions:

Basis Weight

The basis weight of a paper is the designated fixed weight of 500 sheets, measured in pounds, in that paper’s basic sheet size. It is important to note that the “basic sheet size” is not the same for all types of paper.

Caliper

Caliper refers to the thickness of a sheet of paper expressed in thousandth of an inch. This measurement is taken with a micro meter. Normally, paper caliper should not have more than a + or – 5% variance within a sheet. Generally, the relation between caliper and basis weight …. the greater the caliper (the thicker the paper), the greater the paper weight.

Equivalent Weight

While different paper types have different basic sizes, papers can still be compared by using equivalent weight.

Basis Weight (“Category”) Table

The Values in the table below are intended to serve as a guide only.
They should not be used as specifications because there are variances
within the same basis weight due to other characteristics of the papers.
Similar weight papers may vary between different paper manufacturers.

• The darker colored boxes above represent the
  “most common paper weights” for that category.

   

• Normal paper manufacturing tolerance within a
  paper production run is + or – 5% to 7% caliper

   

• This Table was compiled by Micro Format, Inc.
• Copyright 1997-2005 Micro Format, Inc.

  This table may be duplicated with permission from Micro Format, Inc.

International Metric Paper Sizes – ISO Standard