Concrete mixes are designed by following a sequence of steps that take advantage of the qualities of the available materials to make a mixture suitable for the work. The goal of mix design is to estimate the required batch weights of each material that will go into a cubic yard of concrete. Selecting proportions involves balancing economy and meeting the requirements for strength, consistency, placeability, density, appearance, and durability. These characteristics are governed by the intended use of the concrete, expected conditions at the time of placement, and job specifications. Job specifications also may dictate requirements for strength, slump, air content, maximum water-cement ratio, minimum cement content, and maximum size of aggregate.