Estimating a concrete slab

Order concrete from the inside of the forms. Length and width in feet, thickness in inches, then convert. A cubic yard is 27 cubic feet, which is easy to under-order if the thickness is treated as feet.

Four inches is a common patio thickness. It is not a driveway design. If the slab will carry vehicles, confirm a thicker section before you trust a 4-inch estimate.

Waste and the base

An uneven base and concrete left in the truck are why a slab estimate adds waste, often around 10%. The slab calculator starts there. A small equipment pad is different: use the pad calculator if you also need the gravel under the concrete.

Bags make sense for a very small pour. A larger slab is usually ready-mix, and the yard quantity is the number to take to the plant.