Definition:
The thickness of a sheet of paper is indicated by its weight, measured either in grams per square meter (gsm) or pounds per ream (lb). The standard weights of machine-made paper are 190 gsm (90 lb), 300 gsm (140 lb), 356 gsm (260 lb), and 638 gsm (300 lb). It's generally recommended that paper less than 356 gsm is stretched before use to prevent it buckling or warping.
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