Sure, I’m genuinely curious. 
I’m thinking more and more in gsm, as it’s unambiguous. Those imperial people keep on saying “80lbs” and “90lbs” as if it means something (and it sometimes does) but in practice I just find it real confusing, because they basically never mention if it’s cover or text or bristol or frigging liverpool or whatever it is.
So far, I’m looking at 240gsm for the calendar, as that’s what one photo shop advised me to use, but a friend who used to do a lot of print stuff says 200gsm should be enough. I have made prints with 148gsm and they do feel a little too flimsy for something that will be hooked to a nail for a year…