Concrete Columns?
I am building a deck using 8" sonatube 4 ft deep. I need to figure out how many 80lb bags of ready mix concrete to buy to fill each tube.Can you tell me how I determine this number. There are 12 tubes to be filled all together. Thank you.

Well the formula for the area of a circle is:
Pi X radius squared which in your case would be, radius 4" or .34 squared = .1156 pi = (3.142) 3.142 X .1156 =.3632 .3636 X 4' of depth of tube = 1.45 cubic feet per tube 1.45 cubic feet per tube X 12 tubes = 17.43 cubic feet. How many cubic feet are in an 80 lb. bag of sacrete I have no clue, but it should be listed on the bag. If I were you I would get a few extra bags, it is surpising how much you can loose on the ground when filling those things. Tom Somebody check my math please. :) I have been known to order way too much, and way too little concrete. Just ask the dispacthers. :) 
That sounds pretty good to me, but rounding your #'s off makes it a little off. I came up with 16.75404 cu. ft. I Would just say that it takes 2.4 bags per pier x12=28.8 bags. Plus whatever waste you want to account for.....
Bob 
Too many decimal points for me Bob. :o
Thanks for the verification. :) Tom 
concrete colums
thanks for you help, I will buy extra for waste like you said. What a great forum.

TGEB ? Concrete Colums.
after reading your reply, I was wondering why you used a radius of 4" wouldnt I use 8"? since the tubes are 8". I am not questioning your knowledge, just want to be able to figure this out on my own if needed. Thank you again for your help...

8" is the diameter of the tube, 1/2 of the diameter would be the radius, 4" :)
Tom 
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