Concrete is sold by the cubic yard, therefore when preparing to pour a concrete slab it's important to measure the cubic yardage of the space the concrete will go in. Whether pouring concrete for a patio, basement, shed or any other construction foundation, the calculation for determining concrete slab yardage is always the same and can be figured out with relative ease.
Measure the length of the space the concrete slab will be poured into.
Measure the width of the space.
Calculate the area of the space for the concrete slab by multiplying the length by the width. For example, if the length is 10 feet and the width is 10 feet, then the area is 10 feet x 10 feet, which is 100 feet.
Calculate the volume of the space the concrete slab will go in by multiplying the area of the space by the depth of the space.
Generally concrete slabs are poured to a thickness of 4 inches (0.33 feet) or 6 inches (0.5 feet). If the depth of the area is 6 inches and the length and width are each 10 feet, then the volume will be 0.5 feet x 10 feet x 10 feet, which equals 50 cubic feet.
Calculate the concrete slab yardage by dividing the concrete slab feet by 27. Concrete is sold by the cubic yard, which is 3 feet by 3 feet by 3 feet, or 27 cubic feet. To determine how many cubic yards of concrete you need, otherwise referred to as slab yardage, simply divide the cubic footage volume by 27. So if your cubic footage was 50, then your concrete slab yardage will be 50 divided by 27, which is 1.85 cubic yards.
Order slightly more concrete than you calculated for, just to be on the safe side.