When preparing to pour concrete it's important to accurately measure the area of the concrete slab you'll be creating. Whether calculating the area of concrete needed for a patio, shed floor, basement or any other surface, doing the math correctly before you get started can save you time and money. The equation for determining the area of a concrete slab is the same for any project and can be calculated with relative ease.
Determine the length of the space the concrete slab with go in. If the area is an odd shape with more than four sides, you may have to divide it into sections that can be easily delineated and later added together.
Calculate the width of the space for the concrete slab.
Multiply the length by the width to calculate the area of the space for the concrete slab. For example, if the area is 10 feet x 10 feet then the total area for the concrete slab will be 100 feet.
Multiply the area of the space by the depth of the planned concrete slab to calculate the volume of the space the concrete slab will go in.
As a general rule concrete slabs are poured to a thickness of 4 inches (0.33 feet) or 6 inches (0.5 feet). If the depth of the slab you wish to pour is 6 inches and the dimensions of the space are 10 feet x 10 feet, then the volume of the space will be 0.5 feet x 10 feet x 10 feet = 50 cubic feet volume.
Calculate how many cubic yards of concrete you need, since that's the unit in which concrete is sold. A cubic yard is 3 feet x 3 feet x 3 feet, or 27 cubic feet. Since you've measured the volume of the space needed for your concrete slab in feet, you'll need to divide that number by 27 to determine how many cubic yards of concrete you need to order. 50/27 = 1.85 cubic yards.
Order slightly more concrete than you calculated for in case you need extra.
Double-check your calculations by using an online concrete slab calculator, such as the one available on concretenetwork.com.