Paper Weight Converter

US basis weight is defined as the weight of 500 sheets at that paper category's own traditional parent sheet size, and bond, text, cover, and index paper each use a different parent size (17x22 for bond, 25x38 for text, 20x26 for cover, 25.5x30.5 for index). Since the ream weight depends on both the paper's density and the area of 500 of those specific sheets, the same GSM produces a different pound figure in each category purely because the reference sheet size differs, not because the paper itself changes.

Using this calculator's bond conversion factor, 120 GSM works out to approximately 32 lb bond, so yes, those two specifications describe essentially the same paper density. The safest practice when communicating with a printer, especially internationally, is still to specify GSM directly rather than a pound weight, since pound weight is meaningless without also stating which paper category (bond, text, cover, or index) it refers to.

Text/book paper's parent sheet size (25x38 inches) is considerably larger in area than bond paper's parent sheet (17x22 inches), so 500 sheets of text stock weigh substantially more than 500 sheets of bond stock cut from the same GSM paper. The conversion factor this calculator applies to text weight is roughly 2.5 times the bond factor, which is why a 120 GSM sheet reports as roughly 32 lb bond but around 81 lb text -- both numbers describe the identical physical sheet.

The caliper figure here is a general industry approximation, not a lab measurement, because actual sheet thickness depends on the paper's fiber furnish, bulk (how tightly or loosely the fibers are pressed), coating, and finishing process, not on GSM alone. Two different 120 GSM papers -- an uncoated bulky text stock versus a dense coated cover stock -- can measure noticeably different actual calipers on a micrometer despite sharing the same weight-per-area, so treat this number as a starting estimate rather than a spec-sheet-accurate figure.