Estimating concrete involves including a number of factors, most predominately an understanding of the area to be paved. Understanding the cost of the concrete will give you an idea of how much the material will cost, but should not be treated as the final cost since many other factors must be accounted for throughout the installation process.
Things You'll Need
 Calculator
 Tape measure

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 4inches (or .35feet) 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.
References
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