i would really go about looking into the strength test or something. innovator is right on about the subject. i surely wouldnt suggest using any random guess someone made up here that never done anything like this their self.
if 24 - 30 inches tall = 3/4 inch thick the couple guesses i would think are way off.
after a quick search i found this site.
put in the numbers i think are right and it said 3 inch. again i would do what innovator said and call and ask people who have done this before.