Measure the area where the concrete slab will be poured to determine its length and width. If it is irregularly shaped, take the measurements at the widest width and the longest length.
Using the measurements arrived at in Step 1, multiply the width times the length to arrive at the total square footage of the planned concrete slab.
Decide or determine the depth to which the slab will be poured and leveled.
Divide the depth of your proposed concrete slab into the number 320.
Divide the total square feet of your proposed concrete slab by the figure you arrived at in Step 4. The resulting figure will be the amount of concrete needed for your proposed slab, expressed in terms of "yards of concrete," the standard measure in the industry.