How to Calculate Concrete Cubic Yards for Slab

Rectangular Slab

• 1

  Measure the length and width of a rectangular or square slab in feet, using a tape measure.

• 2

  Multiply the length by the width and divide by 9 to calculate the square yards.

• 3

  Divide the thickness of the slab in inches by 36. Multiply the result by the square yards from Step 2 to calculate the total cubic yards of concrete that you need.

Other Slab Shapes

• 4

  Divide the diameter of a circular slab by 2. Square the result, then multiply it by 3.14. The result is the size of the slab in square feet. Calculate an L-shaped slab as if each part of the L were a separate rectangle, then add the two results together. If the slab is an irregular shape, draw it on graph paper so that one square on the paper equals one foot and count the number of squares it contains to figure the number of square feet.

• 5

  Divide the result from Step 1 by 9 to convert the size in square feet to square yards.

• 6

  Divide the thickness of the slab in inches by 36. Multiply the result by the square yards from Step 2 to calculate the total cubic yards of concrete that you need.

Footings

• 7

  Multiply together the width, length and height of each footing in feet, to calculate the cubic feet of each footing.

• 8

  Divide the cubic feet by 27 to calculate the cubic yards of one footing.

• 9

  Multiply the result from Step 2 by the number of footings to calculate the total cubic yards of concrete for all the footings. Add the result to the concrete necessary for the slab itself to calculate the total concrete for the job.