Ed #12 Standards

In addition to size, you also need to consider a paper’s weight.

In North America, printing papers are usually classified by basis weight, which is the weight in lbs. of a ream of paper (500 sheets) in the basic size of that grade. That’s where things can begin to get complicated. Basic sizes are usually not the size of the finished, printed, sheet of paper, but rather the size of the sheet from which the finished paper is cut. So if you buy a 70 lb. paper for use in an 8.5” x 11” brochure, for example, it does not mean that 500 sheets of the 8.5” x 11” paper weigh 70 lbs. Rather, the 70 lb. weight refers to 500 sheets of the basic 25” x 38” sheet size from which the smaller sheets were cut.

To make things more complex, basic sizes are not the same for all grades of paper. Book papers, including coated text and offset papers have a basic size of 25” x 38”. The basic size of bond and ledger writing papers, 17” x 22”, allows for four 8.5” x 11” sheets. Coated and uncoated cover papers have a basic size of 20” x 26”, and other papers have other basic sizes.

Because of these variations in size, papers that have the same basis weights may not look and feel the same. A sheet of 70 lb. text stock, for example, will feel and look much lighter than a sheet of 70 lb. cover. To make things more complicated still, size and weight tables and price lists usually do not refer to a 500 sheet ream, but to the paper’s “M” weight, which is the weight in lbs. of 1,000 cut sheets of the paper.

The ISO standards that are widely used outside North America rely on a different measuring system. Basis weights are expressed in grammage, or the weight in grams of one square meter (g/m² or gsm) of the paper, regardless of its grade or finished size.

Paper weight is important because it helps to determine the project’s quality and feel, the type of presses used and the project’s costs. Almost always, heavier weight papers feel richer and more luxurious than their lighter weight counterparts and can stand up better to the handling they might receive in the mail. Heavier weight papers can also carry more ink as well as varnishes and other coatings. Print show-through is virtually eliminated.

The weight of the paper also comes into play when determining the type of press to be used. To accommodate their high speeds, web presses typically must use lighter weight stocks—50 lb. basis weights or less—and rarely can print anything heavier than a 100 lb. coated, or 80 lb. uncoated cover. Although they run more slowly than most web presses, sheetfed presses can handle heavier weights of paper and a wider variety of textures. Digital presses usually fall somewhere in the middle, with some models able to handle anything from 16 lb. bond up to a 130 lb. cover.