Calculating your concrete requirement.
Calculating the amount of concrete you require for your project can be confusing.
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).
You can obtain a free download of a concrete calculator for your home PC.
Concrete volume formulas.
Square or Rectangle Concrete Slab:
Following are the formulas to calculate how much concrete you will require for a square or rectangular shaped pour:
L x W x T ÷12 = 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
L = Length in feet
W = Width in feet
T = Thickness in inches
CF = Cubic feet of concrete
Example
A patio 10' long by 8' wide - 6" thick
10 x 8 x 6 ÷ 12 = 40 cubic feet of concrete
40 ÷ 0.45 = 89 (88.8) 60 lb bags of concrete
40 ÷ 0.6 = 67 (66.7) 80 lb. bags of concrete
40 ÷ 27 = 1.5 cubic yards of concrete
-----------------
Circular Concrete Slab
Following are the formulas to calculate how much concrete you will require for a circular slab:
3.14 x r x r x T ÷ 12 = 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 feet (1/2 of the diameter)
T = Thickness in inches
CF = Cubic feet of concrete
Example
A circle 6" thick where the circle has a radius of 5.5' (11' diameter circle)
3.14 x 5.5 x 5.5 x 6 ÷ 12 = 47.5 cubic feet of concrete
47.5 ÷ 0.45 = 106 (105.6) 60 lb bags of concrete
47.5 ÷ 0.6 = 80 (79.2) 80 lb. bags of concrete
47.5 ÷ 27 = 1.8 cubic yards of concrete
--------------------
Concrete Tube or Column
Following are the formulas to calculate how much concrete you will require for a circle, tube or column shaped pour:
3.14 x r x r x H ÷ 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
Following are the formulas to calculate how much concrete you will require for a square or rectangular shaped pour:
L x W x T ÷12 = 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
L = Length in feet
W = Width in feet
T = Thickness in inches
CF = Cubic feet of concrete
Example
A patio 10' long by 8' wide - 6" thick
10 x 8 x 6 ÷ 12 = 40 cubic feet of concrete
40 ÷ 0.45 = 89 (88.8) 60 lb bags of concrete
40 ÷ 0.6 = 67 (66.7) 80 lb. bags of concrete
40 ÷ 27 = 1.5 cubic yards of concrete
-----------------
Circular Concrete Slab
Following are the formulas to calculate how much concrete you will require for a circular slab:
3.14 x r x r x T ÷ 12 = 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 feet (1/2 of the diameter)
T = Thickness in inches
CF = Cubic feet of concrete
Example
A circle 6" thick where the circle has a radius of 5.5' (11' diameter circle)
3.14 x 5.5 x 5.5 x 6 ÷ 12 = 47.5 cubic feet of concrete
47.5 ÷ 0.45 = 106 (105.6) 60 lb bags of concrete
47.5 ÷ 0.6 = 80 (79.2) 80 lb. bags of concrete
47.5 ÷ 27 = 1.8 cubic yards of concrete
--------------------
Concrete Tube or Column
Following are the formulas to calculate how much concrete you will require for a circle, tube or column shaped pour:
3.14 x r x r x H ÷ 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
Books on concrete:
Concrete Countertops: Design, Form, and Finishes for the New Kitchen and Bath
Amazon Price: $19.77 (as of 10/11/2008)
Reinforced Concrete: Mechanics and Design (5th Edition)
Amazon Price: $144.00 (as of 10/11/2008)
Working with Concrete
Amazon Price: $13.57 (as of 10/11/2008)
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