Concrete is often used to construct curbs and gutters by filling trenches with concrete to create them. Concrete is sold by cubic yards; so when calculating how much concrete you need to purchase for a project, you must find out how many cubic yards you need. You can do this by finding the area to be filled in feet and then converting that measurement to yards.
Know that the formula for calculating concrete is the following: ((Length X Width X Height)/27) X 1.05 = Total concrete needed plus 5% extra. The length, width and height are measured in feet and then divided by 27 to convert the cubic feet to cubic yards since concrete is sold in cubic yards. The figure of 1.05 is included because it is usually recommended that you purchase 5% more concrete than what you need.
Measure the length, width and height of the trench to be filled to create the curb or gutter. For instance, in this example, let's assume that the length of the curb or gutter is 100 feet, the width is 5 feet and the height is 1/3 feet.
Multiply the length times the width times the height to determine how many cubic feet of concrete you need. For instance, in this example, your equation would consist of the following: 100 ft X 5 ft X 1/3 ft = 166.66 cubic feet.
Divide the above product by 27 (3 cubic ft X 3 cubic ft X 3 cubic ft) to determine the number of cubic yards of concrete you need to make your curb or gutter. In this example, you would complete the following: 166.66 cubic ft/27 cubic ft = 6.173 cubic yards.
Multiply the cubic yards needed to fill the trench by 1.05 to derive the total concrete needed plus 5% extra. In this example, you would complete the following: 6.175 X 1.05 = 6.481 cubic yards.