Basis Sizes and Weights.
Version of 21 July 2006.
Dave Barber's other pages.

With nearly every kind of paper is associated a basis size, which is determined by the manufacturing process, the purpose of the paper, and industry tradition. The weight in pounds of one ream (500 sheets) of the paper in the basis size is known as the basis weight or substance number. For instance, 500 sheets of 17 x 22 inch "substance twenty" bond paper weighs twenty pounds.

Note that the basis weight depends on the standardized basis size, and is not affected by the actual dimensions into which the sheet is cut. Example: the basis size of ordinary 8.5 x 11 inch bond paper is still 17 x 22 (see chart below), and the basis size of 8.5 x 11 cover stock is 20 x 26; this is true even though 20 x 26 sheets cannot be cut into 8.5 x 11 sections without waste.

These basis sizes are based upon British tradition, although today nearly everyone outside the United States uses grams per square meter ("grammage").

Confusing the issue somewhat is that some manufacturers also give what is called the M weight, which is the weight in pounds of one thousand sheets of paper in the size actually furnished, as distinguished from any basis size.

The basis weight is only a rough indicator of how thick the paper is, because the raw materials vary from stock to stock, and some papers are compressed more than others in manufacturing.

The six common basis sizes in the United States:

Size (inches)Area (square inches)Examples of Paper Using this Basis
17 x 22 374Bond, Ledger, Mimeograph, Photograph, Writing
20 x 26520Cover Stock
22.5 x 28.5641.25Bristol Board
25.5 x 30.5777.75Index Stock
24 x 36 864Tag, Newsprint, Tissue, Wallpaper, Wax Paper, Wrapping Paper
25 x 38 950Text, Offset, Book, India

Basis sizes less frequently used:

Size (inches)Area (square inches)Comments
12.75 x 16204United States Currency
20 x 20400Chemical Filter Paper
19 x 24456Blotter Paper
20.5 x 24.75507.375The former Index basis
18 x 31558Manuscript Cover
20 x 30600Carbon Paper
21 x 33693Wedding Invitations
22.5 x 35787.5Occasionally used for Bristol

From time to time, a basis size of 32 x 44 inches is encountered; it has the special property that the number of pounds in the basis weight is equal to the number of grams per square meter.

Equivalence Chart for Basis Weights

Read across each row to find different designations for the same weight of paper. For example, 28-pound bond, 58-pound index and 70-pound text all weigh 104 grams per square meter.

Underscored are the most popular designations of printing or writing paper; utility papers run anywhere between 20 and 500 grams per square meter.

These figures are consistent within three percent. We have not attempted a greater precision because:

Basis Weight in Pounds Grams
Per
Square
Meter
Bond
17 x 22
Cover
20 x 26
Bristol
22.5 x 28.5
Index
25.5 x 30.5
Tag
24 x 36
Text
25 x 38
16 22 27 33 37 40 60
20 28 34 41 46 50 75
24 33 41 50 55 60 89
26 36 44 54 60 65 97
28 39 48 58 64 70 104
32 44 54 66 73 80 119
33 46 57 69 77 84 125
36 50 61 74 82 90 134
39 54 67 81 90 100 147
41 57 71 86 95 105 155
43 60 75 90 100 110 162
45 63 77 94 104 115 169
47 65 80 97 108 119 176
53 74 91 110 125 135 199
58 80 99 120 133 147 217
65 90 111 135 150 165 244
67 93 115 140 155 170 252
72 100 123 149 166 182 270
76 105 130 158 175 192 284
79 110 136 165 183 201 298
86 120 148 179 200 219 324
94 130 161 195 216 238 352