speaker stand filler follow up

Am hoping some mathematician can assist me in figuring out how much filler I need. PMKably recommended midway usa for lead shot, and they have it! Now I need to determine what guage to buy and how much. My spekaer stands are a triagular column - 20 inches high and the triangles are 4 inches on each of the three sides. Any thoughts on how many pounds of shot I will need to fill these up? Thanks for the help.

Scott