Calculating the amount of concrete you require for a column, sono tube or round footing can be confusing.
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Notes:
- Pre-mix concrete comes in bags that are 60 lbs. and 80 lbs.
- A 60 lb. bag provides 0.45 cubic feet of cured concrete.
- A 80 lb. bag provides 0.6 cubic feet of cured concrete.
- If you have concrete delivered it is sold by the yard (which is a cubic yard = 27 cubic feet).
Following are the formulas to calculate how much concrete you will require for a circle, tube or column shaped pour:
3.14 x r (inches) x r (inches) x H (inches) ÷ 1728 = cubic feet of concrete (CF)
Number of bags of concrete needed:
CF ÷ 0.45 = number of 60 lb. bags
CF ÷ 0.6 = number of 80 lb. bags
Number of cubic yards of concrete needed:
CF ÷ 27 = cubic yards
r = radius of the circle in inches (1/2 of the diameter)
H = Height in inches
CF = Cubic feet of concrete
Example:
A column 8' high where the column has a radius of 5″ (10″ diameter tube)
3.14 x 5 x 5 x 96 ÷ 1728 = 4.4 cubic feet of concrete
4.4 ÷ 0.45 = 10 (9.8) 60 lb bags of concrete
4.4 ÷ 0.6 = 8 (7.3) 80 lb. bags of concrete
4.4 ÷ 27 = 0.16 cubic yards of concrete