When you take on a do-it-yourself project, you need to know how much material you need before you can begin. Knowing how much of each material you need gives you a base range of the costs for the total project. When working with concrete, you need to know the length and width of the area you're filling, along with the depth. The volume of concrete you need is measured in cubic feet, which can be converted to yards if necessary.
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Measure the length of the area you're filling in using feet. For example, use a concrete area of 15 feet long.
Measure the width, also in feet. Use 10 feet for the width of the slab for this example.
Divide the number of inches of depth of the slab to be poured by 12 to convert it to feet. Assume the thickness is 4 inches for this example, which is equal to 0.333 feet.
Multiply the length, width and depth together. Using the example of 15 by 10 by 0.333 feet, the total volume is 50 cubic feet.
Convert the cubic feet to cubic yards by dividing the feet by 27, which equals 1.85 cubic yards of concrete necessary for the project.