An 80-pound bag of concrete makes 0.6 cubic feet. A cubic foot of any material is enough to fill a box that is 1 foot wide, 1 foot tall and 1 foot long.
In order to determine the volume of concrete required for a project, a worker must determine the surface area and thickness of the concrete. He calculates the surface area by multiplying the length by the width for rectangular projects. The project plans specify the thickness of the concrete. However, before multiplying the surface area in square feet by the thickness in inches, it is necessary to convert all measurements to the same unit. Divide the thickness in inches by 12 to convert it to feet, and multiply by the surface area.