Thus when calculating postage weight by counting the number of sheets you can calculate that, for example, the weight of one A4 sheet is 1/16 the gsm of the paper - 1/(2^4).
http://en.wikipedia.org/wiki/Paper_density#Basis_weight
In order to figure out the actual mass of a sheet of U.S. paper from the reported basis weight, you must know how many sheets of paper were in the "basis ream" and what dimensions they were. The basis ream sheet dimensions may have nothing to do with your final sheet of paper, and the number of sheets varies too.
I know those types of conversations. They stay with you for months and sometimes years, never ceasing to irritate.
When it's the other way round, you can find peace at some point (even if it takes months or years). But if you were the brick wall, it first takes months or years and THEN, when you finally do realize the reality of the situation, it takes even longer to settle. shudders