I work in the fence industry and many times I need to figure out how many bags of concrete I'll need instead of ready-mix truck pours.

I have a simple calculator I use in Excel, the formula is below, the cells it refers to is number of holes, depth and diameter and it outputs cubic yards needed for the job.

I carry this with me on my PDA as well but I found that it is critical for me to find a simple way of calculating 60 and 80 pound bags as well at the same time.

I have found plenty of online calculators such as this one which is awesome: www,decks.com/calculators/concrete.aspx but I really need to know the math behind it

Can anyone help me out with this?

Thanks in advance for any help.

=(B3/12*0.5)^2*(3.14)*(D3/12)*(A3)/27

Holes, Dia., Depth, C.Y. Needed, 60#, 80#, $ Per C.Y., Extended

I have a simple calculator I use in Excel, the formula is below, the cells it refers to is number of holes, depth and diameter and it outputs cubic yards needed for the job.

I carry this with me on my PDA as well but I found that it is critical for me to find a simple way of calculating 60 and 80 pound bags as well at the same time.

I have found plenty of online calculators such as this one which is awesome: www,decks.com/calculators/concrete.aspx but I really need to know the math behind it

Can anyone help me out with this?

Thanks in advance for any help.

=(B3/12*0.5)^2*(3.14)*(D3/12)*(A3)/27

Holes, Dia., Depth, C.Y. Needed, 60#, 80#, $ Per C.Y., Extended

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