The actual size of a CMU is always ____ less than its nominal size.

The correct answer for the actual size of a Concrete Masonry Unit (CMU) being less than its nominal size is 3/8". In the masonry industry, nominal sizes of CMUs are used for design and construction purposes, making it easier to calculate and plan. However, the actual size of these blocks is smaller due to the manufacturing process and the inclusion of mortar joints in construction.

For standard CMUs, the nominal dimensions typically reflect the block's size with the mortar joint accounted for, while the actual dimensions are slightly reduced. Specifically, the industry standard is that the actual dimensions of a standard block are 3/8" shorter in each direction than the nominal size. This results from the typical thickness of the mortar joint, which is usually 3/8".

Understanding this difference is crucial for ensuring that masonry work fits together correctly and that structures are built to the intended design specifications. This knowledge allows masonry professionals to accurately plan the layout and integration of CMUs in construction projects.