With nearly every kind of paper is associated a grammage, basis size, or both, which is determined by the manufacturing process, the purpose of the paper, and industry tradition.
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 81⁄2 × 11 inch bond paper is still 17 × 22 (see chart below), and the basis size of 81⁄2 × 11 cover stock is 20 × 26; this is true even though 20 × 26 sheets cannot be cut into 81⁄2 × 11 sections without waste.
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 (the caliper), because the raw materials vary from stock to stock, and some papers are compressed more than others in manufacturing.
Equivalence Chart for Basis Weights.
In the table below, 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.
Highlighted 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. To attempt a greater precision is not helpful because:
|basis weight in pounds||grams|
17 × 22
20 × 26
221⁄2 × 281⁄2
251⁄2 × 301⁄2
24 × 36
25 × 38