I am definitely not a math whiz so somebody who is needs to check these calculations out before the person goes out and buys ready mix. I used a table I found online suggesting that a 60 pound sack of Sakrete had approximately .45 cubic feet.
1. 70 * .33 to convert to 23.10 cubic feet for the slab
2. 23.10 / .45 to show 52 sacks needed
I just poured three footings that were approx. 2'x2'x1'.
I used 80lb and it took 11 bags.
But you should read the back of the bag.
It will tell you the calculation.
Then just pick up a few extra just in case.
You can always bring them back.
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