Figuring out how much concrete you need for a specific project has been an age-old problem that has made even the most experienced scratch their heads in frustration. The good news is that there is a tried and true method to this problem. There are a few different applications to consider.
Determine the overall length of the concrete to be poured. Using the tape measure, measure the length of the project. If you are pouring footers, then take the combined length of all footers to be poured. If you are pouring walls, then you will also take the length of the walls.
Determine the square footage of the project. To determine the square footage of a project, you will multiply the length by the width. Because walls, footers and pads are calculated a little differently, you will need to follow the steps below as they apply to your individual needs for cubic yards of concrete.
Figure the amount of concrete in a concrete pad. Concrete pads are usually poured for the purpose of parking or for a base for a storage building. To figure the yards of concrete necessary to pour a concrete pad, take the square footage of the pad (length time width) and multiply that by the thickness of the pad. Because we are working in feet and not inches, you must convert everything that is below 1 foot into fractions. A pad will usually be 4 inches, 6 inches or 8 inches. For example, 4 inches is 0.33 of 1 foot. So, for a 4-inch pad that is 10 feet by 10 feet, you would do the following: 10x10x0.33=33. To convert that into cubic yards of concrete, you must divide that number by 27 and that equals 1.222 yards of concrete.
Figure out the concrete you need for a footer. To do this, take the overall length of the footers, multiply that by the width of the footer (if the footer is 16 inches wide, then that will be 1.33), and multiply that by the thickness of the footer. If the footer is 8 inches thick, then you will convert that 8 inches into 0.75. So, for example, if your footers are 100 total feet long, 16 inches wide and 8 inches deep, then you will do the following: 100X1.33X0.75= 99.75 cubic feet to be filled. Now, to convert that into cubic yards of concrete, divide that number by 27 and that comes to 3.694 yards of concrete.
Figure out the amount of concrete necessary to fill a block wall. Multiply the length by the height by the thickness of the wall. For example, the thickness of an 8-inch block wall will not be 8 inches. You must consider that the space inside a block is approximately 6 inches instead of 8 inches. So, for an 8-inch block wall that is 100 feet long and 4 feet high, multiply 100 by 4 by 0.5(6 inches), and you get 200 cubic feet. Then, divide that number by 27 to get cubic yards of concrete and you get 7.40 cubic yards of concrete.