Pouring a slab for your foundation, driveway or sidewalk starts with estimating the amount of concrete you will need for the job. Estimating the number of square feet your project will cover is usually easy but meaningless when you discover that concrete is sold by the cubic yard. You can make the conversion yourself and save the time and aggravation of a professional estimate if you grab a calculator.
Things You'll Need
 Measuring tape
 Calculator

Measure the surface area of your project.

Determine the depth of your slab.

First calculate the total square feet. For a 30X50foot slab, multiply 30 by 50 to get 1,500 square feet.

Multiply the depth of the slab by the square footage. Continuing the example above, for a 6inch slab, multiply 1500 by 0.5 to get 750 cubic feet.

To get cubic yards, divide your answer by 27 (the number of cubic feet in a cubic yard). For our example: divide 750 by 27 to get 27.7.
Tips & Warnings
 Convert inches to decimal fractions by dividing the number of inches by 12 when the depth is less than one foot. For example, 8 inches = .666, 10 inches = .833.
 If you don't want to do the math yourself, several online calculators are available. Try the links in Resources.
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References
 Photo Credit foundation steel. image by Greg Pickens from Fotolia.com