Basis weight of paper

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The weight of paper is commonly expressed as its basis weight: the weight, in pounds, of a ream of standardized dimensions and sheet count. The standard dimensions and sheet count of a ream vary according to the type of paper. For example, a sheet of common copy paper that has a basis weight of 30 pounds does not have the same mass as the same size sheet of coarse paper. In the former case, the standard ream is 500 sheets of 17 by 22 inch paper, and in the latter, 500 sheets of 24 by 36 inch paper.

Historically, this convention is the product of pragmatic considerations such as the size of a sheet mold.

Sheets 17 by 22 can be cut into four 8.5 by 11 inch sheets, a standard for business stationery. So, the 17 by 22 inch ream became commonly used. The 25 by 38 inch book-paper ream developed because such a size can easily be cut into sixteen 6 by 9 inch book-sized sheets without significant waste.

Early newsprint presses printed sheets 2 by 3 feet in size, and so the ream dimensions for newsprint became 24 by 36 inches, with 500 sheets to a ream. Newsprint was made from ground wood pulp, and ground wood hanging paper (wallpaper) was made on newsprint machines. Newsprint was used as wrapping paper, and the first paper bags were made from newsprint. The newsprint ream standard also became the standard for packaging papers, even though in packaging papers kraft pulp rather than ground wood was used for greater strength.

Much of the world has adopted the metric system and uses grams per square meter as the units expressing the standard basis weight of all types of paper and paperboard.

Here are some basic ream sizes for various types of paper. Units are inches except where noted.