Aquarium Sizes and Weight Chart
Maybe this will help. I've actually checked it out with my 5 gallon and 10 gallon and it's pretty accurate (at least for those two).
Take into consideration you are taking the
weight of your aquarium (filters, hood, tank, lights) + amount of water actually in it (displacement) + decor + fish + your stand +any supplies in your stand = total amount
Also, if your stand has feet, (4 points) you might want to set it atop something (like a piece of plywood) to help distribute the weight.
I would be nervous about 2nd floor stuff, but that's just me.