Actually it's 8.6lb/us gallon, but that's not the point. You have to add in the weight of the stand, glass, substrate, filters, tops, decorations and lights. You can go all out and measure the weight of each one of these components if you want to, but the 10lb per gallon estimate is very good for a running aquarium.
CB, please keep the number of new threads to a minimum if they are on the same subject. It's always better to post in an existing thread than start a new one. Everyone else: If you have nothing constructive to say, then move on. This is the last warning. If I have to deal with this mess again, it's time for some bans.