Density is the weight per unit volume of a material and is a property of raw materials measured in pounds per cubic foot (lb/ft3). The weight of a wall, roof, or floor is equal to its volume times its density. Most concrete has a density of 140 lb/ft3, but when steel reinforcing is added the density increases to 145 to 150 lb/ft3. The clay material used to make typical bricks has a density of about 120 lb/ft3. The density of concrete used to make concrete masonry units varies from 85 to 135 lb/ft3. as the material is fabricated into masonry units or bricks, the density of the basic material is unchanged, but the unit weight of the finished product can be lower because of cores in the final product. A cubic foot of a concrete block wall includes the hollow cores as well as the solid material, and so its unit weight is lower than that of a cubic foot of solid concrete. For two material samples of equal weight, the denser material will occupy a smaller volume. For two samples of the same volume, the denser will weigh more.