Grammage and Basis Weight
I usually reserve Friday’s post for things I’m learning in class but school is officially out for the summer. Summer Fridays will be a bit of a grab bag – there’s plenty of paper stuff out there to choose from. One of my goals for the summer is to study up on paper properties so you can count on Fridays having a good dose of definitions, starting today with grammage and basis weight!
Grammage is the mass of a sheet of paper divided by the area of the same sheet of paper and is expressed in grams per square meter (g/m2). Grammage is a key determinant in the selling price of paper. Several other paper properties (e.g. bursting strength, thickness and bulk) are defined with regard to grammage. In the United States, mass per unit area is also expressed as basis weight. Basis weight is calculated based on the weight in pounds of a ream of paper of specific size and number, which is usually 500 sheets although sometimes 480 sheets. The grammage of paper is controlled primarily by the loading of fiber stock onto the paper machine but is also affected by fillers, coatings, sizing and the end moisture content of the paper.
For testing method see TAPPI T-410; Grammage of Paper and Paperboard
The Weyerhaeuser site features these conversion calculators:
Basis Weight from Grammage
Grammage for a Basis Weight
Also, this image from thepapermillstore.com is helpful and lists both grammage and basis weight:
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