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Those Tricky Paper Weights

Definition of Weights
Stock designations in printing can be very confusing. For instance, a printer may use 60# offset stock for letterhead or a 24# bond stock. In actual fact, 24# bond, and 60# offset weights are approximately the same. But the offset stocks are generally for full color printing, while bond stocks are more often used for one and two color printing.
Caliper refers to the thickness of a sheet of paper expressed in thousandth of an inch. This measurement is taken with a gadget called a micro meter. Normally, paper caliper should not have more than a + or - 5% variance within a sheet.
It isn't practical to talk about the weight of a single piece of paper, so the 500-sheet ream is the unit that has been chosen for comparisons. Americans designate by "basis weight" which is calibrated on how much a ream of that particular paper weighs when cut to it's basis size. The basis size varies by category of paper.
Most of the rest of the world generally designates "grammage" which is grams per square meter. .
Paper weight is sometimes stated using the "#" symbol. For example, "20#" means "20 pounds per basis ream of 500 sheets".
To confuse the issue even more, paper is generally designated by weight while cardstock is designated by thickness.

Definition of terms
Grain: When printers are designating paper, they also take into account which direction the grain is running which is the direction most fibers lie in a sheet of paper. For example, with bottle labelling it is essential that labels are produced with grain running left to right, otherwise the labels might peel off the bottles. Grain direction can and does have an effect on some laser printers, so its best to be aware.
Regarding the terms in the chart below:
Bond paper: writing paper and reprographic paper used for letterheads and business forms. It is manufactured at 17" x 22" and cut down from there. (It's name is derived from the original use of such paper for government bonds.)
Offset paper: more resistant to water than bond so it dries quickly and less susceptible to "picking" (Where tiny bits of the surface of the paper may come off while printing).
Cover weight: generally used for the cover of books, pamphlets, or other soft covered books.
Tag: strong, heavy paper calendered (flattened) to a smooth hard finish.
Index paper: heavy, stiff paper characterized by bulk and strength; includes index and printing bristols.
This chart will help you sort out how the designation of one category of paper compares to another.
 
The blue numbers indicat the most common weights offered in each category.

 

Weight and thickness equivalents for paper stocks

Bond
Offset
Cover
Tag
Index
 
Points
Thickness
Lbs
Lbs
Lbs
Lbs
Lbs
sp2
sp2
Inches
16
40
22
37
33
sp1
3.2
.0032
20
50
28
46
42
 
3.8
.0038
24
60
33
56
50
 
4.8
.0048
28
70
39
64
58
 
5.8
.0058
29
73
40
62
60
 
6
.0060
36
90
50
82
75
 
6.8
.0068
43
110
60
100
90
 
7.4
.0074
47
120
65
108
97
 
8
.0078
53
135
74
122
110
 
9
.0085
54
137
75
125
113
 
9
.009
58
146
80
134
120
 
9.5
.0092
65
165
90
150
135
 
10
.0095
67
170
93
156
140
 
10.5
.010
72
183
100
166
150
 
11
.011
76
192
105
175
158
 
13
.013
82
208
114
189
170
 
14
.014
87
220
120
200
180
 
15
.015
105
267
146
244
220
 
18
.0175

Although every effort is made to remain current, Tarvin Commercial Art does not warrant the accuracy of data detailed herein.

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