How to Determine Cement Per Cubic Yard

Concrete is a mixture of four components that, when combined, harden to withstand crushing forces of up to 4,500 pounds per square inch (psi) or more. The four components of concrete are cement, coarse aggregate rock, wet sand and water. In a cubic yard of concrete, approximately 15 percent will be composed of cement, 38 percent of coarse aggregate rock, 38 percent wet sand and 8 percent water. These numbers will fluctuate based on rock size because smaller rock sizes will require more cement than larger rock sizes.

Instructions

- 1
  Establish the maximum size aggregate you'll be using in your concrete mixture. Sizes range from 3/8 inches to 1 1/2 inches in diameter. Suppose you're using the middle size, 3/4 of an inch, for your calculation example. Finally, because one 94-lb. bag of cement is one cubic foot of bulk material, you can label a cubic foot one "part." In this example, one "part" -- be it cement, rock, sand or water -- is equal to one cubic foot of that material.
- 2
  Add one part cement, 2 1/2 parts 3/4-inch coarse aggregate rock, 2 1/2 parts wet sand and 1/2 part water. This mixture will contain a total of 6 1/2 parts. Because the approximate final volume of concrete is 2/3 of the sum of its parts, you know that these 6 1/2 parts equate to 4.3 cubic feet of concrete (6.5 times 0.66).
- 3
  Divide 27 (the total number of cubic feet in 1 cubic yard) by 4.3 to determine the number of mixed batches of concrete you'll need to reach one cubic yard. In this example, it would be 6.3 batches, where each batch contains one cubic foot of cement. Therefore you can determine that one cubic yard of concrete contains 6.3 cubic feet of cement.

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