Paper - The Graphic Design: Reference and Specification - page 67

c a l i p e r , b u l k , a n d p p i
Paper thickness is defined as caliper. Caliper is measured in thousandths of an inch and
expressed as point size. One point equals 0.001 inch. Stock that is 0.007 inch thick is
described as 7 point or 7 pt. Points are most often used when referring to cover stock.
It is also used by the U.S. Postal Service, which states its thickness requirements in
calipers.

The term bulk is used to refer to the thickness of paper relative to its paper weight. A
paper's finish will have an impact on its bulk. For instance, coated papers tend to be
thinner than uncoated papers and have less bulk for their basis weight.

Publishers often state bulk as pages per inch, or ppi. Below is a comparison chart that
compares caliper size with pages per inch.

Caliper Pages per inch (ppi)

0.0020 1000

0.0024 842

0.0028 726

0.0034 592

0.0038 532

0.0042 470

0.0046 432

0.0050 400

0.0054 372

0.0060 332