Determine the area where the concrete will be poured.
Measure the length and width of the area in feet.
Determine the depth of the concrete in feet. A standard slab is 4-inches (or .35-feet) deep.
Multiply the length by the width by the depth to determine the cubic feet of concrete required.
Divide the value by 27 to convert cubic feet into cubic yards.
Add an additional 10% overage to allow for variation and spill.
Multiply by the cubic yards by $105, which is the average cost of concrete in Texas as of July, 2011.