first of all is how good are you at it. do you put on a nice bead or slop it on and all over? How much calk will it take to do a window all depends on the person doing it. I guess you need to know how big of tubes your going to buy little ones or big ones. Maybe you want to measure around a window and then see what the coverage the tube might say. This is one you just might have to figure yourself by how much of a tube your going to use per window then times that many windows. I think 12 tubes will probably do it tho hahah
.
