Making Sense of Paper Weights
We're often asked, "How can 50# offset weigh the same as 20# bond?"
Many people outside the paper industry are confused about "basis weights for different grades of paper. Bases weight refers to the actual weight of 500 sheets of a paper in a specific basis size. For example: 20# bond means that a ream (500 sheets) of 17 X 22 paper wieghs 20 pounds. The confusion arises from the different basis sizes.
Each paper type has its own basis size. The most common types of paper are listed below with their respective basis sizes. These basis sizes have their origins in the long history of paper making and printing.
Paper Type Basis Size
Bond 17 X 22
Book/Offset 25 X 38
Cover 20 X 26
Index 25 1/2 X 30 1/2
Vellum Bristol 22 1/2 X 28 1/2
The chart above tells you that 500 sheets of 65# cover stock, 20" X 26", will weigh 65 pounds. Also, 500 sheets of 67# vellum bristol, 22 1/2 X 28 1/2 will weigh 67 pounds.
Paper comes in sizes other than the basis size. For instance, book paper frequently comes in 17 1/2 X 22 1/2, 19 X 25, 23 X 35, 25 X 38 and sometimes 28 X 40. So you need the concept of a basis size and weight to compare papers.
The chart below is an abbreviated equivalent basis weight chart. From this chart you can see that a sheet of 20# bond weighs the same as 50# offset or 27# cover. In addition, you can see that 60# offset is quite a bit lighter than 65# cover. In fact, 60# offset is equivalent in weight to 33# cover! The numbers in a colored box indicate the most common weights available in each basis size. In other words, you can find 65# cover but you won't find 72# book weight paper.
