Quandaries and Queries


Yes I am having a small problem and being a General Contractor I should know this but for some reason I keep forgetting how to calculate how many yards of concrete it will take to pour a foundation. I have another job coming up soon and need to know how to calculate how much concrete it will take for the foundation. The foundation is 20' X 20' and the depth is 6", there are also three footings that are 20' X 12" X 12" each. Can you show me the equation to figure out how many yards of concrete I will need to pour the footings and foundation. Can you help me please? Thank you very much and have a wonderful day.


Hi John,

From your note that you are pouring a slab that is 20' by 20' and 6" thick and three footings that are 20' by 12" by 12".

First you need to put all the dimensions in the same units. I am going to choose feet. Thus the slab dimensions in feet are 20 by 20 by 1/2. Hence the volume of concrete in the slab is

20 20  1/2 = 200 cubic feet.

One yard is three feet so a cubic yard is three feet by three feet by three feet. 3  3  3 = 27 and hence 1 cubic yard is 27 cubic feet. Thus the volume of concrete in the slab is

 200/27 = 7.4 cubic yards.

In a similar fashion each footing has a volume of

20  1 1 = 20 cubic feet

which is

 20/27 = 0.74 cubic yards.

Thus you need

7.4 + 3 0.74 = 9.6 cubic yards.



Go to Math Central