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econdave 04-07-2006 06:48 PM

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.

tgeb 04-07-2006 07:46 PM

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.


Somebody check my math please. :)

I have been known to order way too much, and way too little concrete. Just ask the dispacthers. :)

bob the builder 04-07-2006 07:59 PM

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.....


tgeb 04-07-2006 08:21 PM

Too many decimal points for me Bob. :o
Thanks for the verification. :)


econdave 04-08-2006 06:08 AM

concrete colums
thanks for you help, I will buy extra for waste like you said. What a great forum.

econdave 04-08-2006 06:33 AM

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...

tgeb 04-08-2006 09:56 AM

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


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