Calculate concrete quantities for large or small concrete jobs based on the square yards of the project. Proper calculations lead to less waste and less risk of not having enough concrete available to complete the project. In addition, when you know how much concrete you need helps with budget planning.
Measure the width, length and depth of the concrete project in feet. If the project is a pad, divide the number of inches by 12 to determine the decimal equivalent of the portion of a foot. For example, a 4-inch thick pad would be .3333 of a foot.
Multiply the width by the length by the thickness of the concrete. For example, a pad that is 16 feet long by 12 feet wide by 4 inches deep would be 16 x 12 x .3333 = 63.99 cubic feet in volume.
Determine the cubic yards by dividing the cubic feet by 27. Using the example, 63.99 cubic feet is equal to 2.37 cubic yards.
An 80-pound bag of concrete is approximately .60 cubic feet of concrete. For a small job, you can calculate the number of 80-pound bags of concrete needed for the project by dividing the number of cubic feet of the project by the number of cubic feet in a bag of concrete. Using the example, 63.99 cubic feet needed for the project divided by .60 cubic feet per 80-pound bag of concrete shows that this project requires 106.656 bags of concrete.
A 40-pound bag of concrete is approximately .30 cubic feet or .011 cubic yards of concrete. A 60-pound bag of concrete is approximately .45 cubic feet or .016 cubic yards of concrete. An 80-pound bag of concrete is approximately .60 cubic feet or .022 cubic yards of concrete.