GSM is the weight of one square metre of paper. It is the single most useful number on a specification sheet, because it predicts how the sheet feeds, how much ink shows through and how the finished document feels in the hand.
diagram — weight comparison
Everyday office printing
For internal documents, 70 to 75 gsm is normally enough. It runs cleanly through most office machines and keeps cost per page down where volume is high.
Documents that leave the building
Quotations, reports and letters read better on 80 gsm. There is less show-through on double-sided printing and the sheet holds its shape in a folder.
When to go heavier
Covers, certificates and presentation material justify heavier stock. Check the machine specification first: not every office printer will take it without adjustment.
