Calculating the Amount of Concrete Needed For Footings
Footings will rarely follow the drawing exactly.
In rocky soil the footings may collapse when big rocks are excavated
This was supposed to be a 12"*12" footing, but note how the left side of the footing has collapsed. Calculate the true width.
The excavator may have dug too deep, or it may have rained and footings needed to be dug out deeper to reach firm soil. So it is important to check a variety of spots on your footing and get an average size. Then use the calculator to figure the amount of concrete needed.
House slabs on grade that are 8" out of grade with a 4" slab also have some of the footing above the grade too.
This 12" x 12" footing needs to be calculated 12" x 16" so the footing is figured to go above grade to reach the 4" slab thickness.