Mailers must use mailpieces constructed from high tear strength paper stock. For envelopes or letter-sized mailpieces sealed along all four sides, mailers must use paper with a minimum basis weight of 50-pound book-grade paper. The conversion table in Exhibit 2-1.2 provides a cross-reference for basis weights of various papers.
Note: In this Publication 25, all references to paper basis weight are for book-grade paper unless otherwise stated.
Exhibit 2-1.2
Paper Basis Weight Conversion Table
Paper basis weight is based on the weight of 500 sheets of one of the following grades of paper:
For example, if 500 sheets of book-grade paper weigh 39 pounds, the paper is considered 39-pound book paper.
Equivalent Values
Book Weight
Bond Weight
Cover Weight
Newsprint Weight
39
15
21
35
40
16
22
36
50
20
27
45
55
30
60
24
33
70
28
64
75
41
68
80
31
44
73
90
82
100
56
91
110
128
116
