Paper Weight GSM Converter
Convert paper basis weight in pounds per ream to GSM and back using the actual basic sheet size and ream count instead of a misleading universal factor.
Convert paper basis weight and GSM
Convert U.S. basis weight in pounds per ream to grammage only when the basic sheet size and ream count are known.
How the Paper Weight GSM Converter works
GSM, or grammage, is mass in grams per square metre. U.S. basis weight is different: it is the mass in pounds of a ream at a paper-grade-specific basic size. The calculator converts the ream mass to grams and divides by the total area of all basic sheets. Reverse conversion applies the same relationship in the other direction.
How to use this paper weight gsm converter
Choose a conversion direction, enter the weight value, then enter the paper grade’s basic sheet width, height and ream sheet count. TAPPI notes that 500 sheets is common but not universal. For example, bond/writing is commonly based on 17 × 22 inches, text/book on 25 × 38, cover on 20 × 26 and index on 25.5 × 30.5.
How to interpret the result
The same “80 lb” label can represent very different GSM values because the basic sheet area changes by grade. That is why a paper converter that asks only for pounds and returns one fixed GSM number can be wrong. The basic-sheet area shown in the result makes the conversion basis auditable.
Assumptions and limitations
This is a mass-per-area conversion, not a thickness calculator. Paper caliper varies with furnish, coating, density and manufacturing. Confirm the grade’s basic size and ream convention from the mill, merchant or applicable standard before using converted values in purchasing specifications or press settings.
Practical example and workflow
An 80 lb text/book stock using a 25 × 38 inch, 500-sheet basis converts to roughly 118 GSM, while 80 lb cover uses a 20 × 26 basic size and is much heavier per square metre. The calculator exposes that difference instead of treating both 80 lb labels as equivalent.