Trying to convert 135g/m2 paper to pounds (European to U.S.)
For "bond" (copy paper, stationery and the like) divide by 3.76 (and round). 135 gsm paper is 36# by US measure.
The weight of US paper of 500 sheets of basis sheet. Basis sheet is not what you use (like US letter, 8.5" x 11") but what it is cut from. The bond basis sheet is 17" x 22" so 187000 inČ weighs would weigh the specified weight, 36 pounds in this case. (I never said it made sense, just that there is a way)
Different kinds of paper, tag, index, newsprint, etc have different size basis sheets (use Google) so weights can't be compared directly. Each type has its own conversion to gsm.