About this tool
The Paper Weight Converter translates paper weight between GSM (grams per square metre) and the US basis-weight system measured in pounds. GSM is a universal, unambiguous figure — it is simply the mass of one square metre of the sheet. US basis weight, by contrast, is the weight of 500 sheets (a ream) cut to that stock's traditional basis size, so the same 'lb' number means different things for bond, text, cover or index paper. This tool removes that confusion by letting you pick the stock type explicitly.
The conversion is a single multiply: GSM = lb × grammage factor, and lb = GSM ÷ grammage factor. Each stock has its own factor derived from its basis-sheet dimensions — Bond/Writing (17×22 in) = 3.7607, Book/Text/Offset (25×38 in) = 1.4805, Cover (20×26 in) = 2.7048, Index (25.5×30.5 in) = 1.8039, Tag (24×36 in) = 1.5714, and Bristol (22.5×28.5 in) = 2.1930. The tool reports the converted weight along with the basis sheet size and factor it used, so the result is transparent.
Everything runs locally in your browser — no data leaves the page. Pick a direction and stock type, type the value, and read the equivalent instantly. This is handy when a spec sheet lists '80 lb cover' but your supplier quotes GSM, or when comparing papers sold under different regional conventions.