How to Calculate Concrete for a Semicircle Driveway

Calculate the amount of concrete necessary for your semicircle driveway by recognizing that the driveway's shape is that of a half cylinder. The shape of the concrete slab can be visualized as cutting of a 6-inch tall cylinder in half through one of its two circular sides. Volume measures the amount of space a given object occupies and for a semicircle this depends on the concrete slab's thickness and the length of the straight portion. The length of the straight portion is the width of the circle or diameter. Half of the diameter distance equals the radius.

Calculator
Tape measure

Instructions

- 1
  Measure the depth of the space the concrete will fill in inches. This is the same as the concrete slab's thickness. Assume this measurement equals 6 inches for the example calculation.
- 2
  Measure the length of the straight portion of the semicircle in inches. This is the diameter of the semicircle. For the example, use a diameter of 120 inches.
- 3
  Calculate the radius of the semicircle in inches by dividing the diameter by two. This results in 120 divided by 2 or 60 inches for the radius.
- 4
  Convert the radius and thickness measurements to feet by divided by 12, since a foot contains 12 inches. Continuing the example you have 0.5 feet and 5 feet for the thickness and radius respectively.
- 5
  Multiply the number pi by the thickness and by the square of the radius then divide by 2 to obtain the amount of concrete required in cubic feet. Use 3.14 for the number pi. Now, for the example you have 3.14 times 0.5 feet times ( 5 feet )^2 or 39.25 cubic feet. The symbol "^" represents an exponent and is read as "to the power." Lastly, dividing by two leads to 19.63 cubic feet. The example project requires you to buy 20 cubic feet of concrete.

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