What are the average dimensions of concrete blocks?

In the United States, concrete blocks most commonly measure 16 inches long, 8 inches high and 8 inches deep. The actual dimensions of the blocks are smaller by three-eighths of an inch to account for the standard width of a mortar joint.

Concrete blocks, sometimes called concrete masonry units, come in a variety of depths to accommodate walls of different thicknesses, but the most common depth is 8 inches. In addition to the standard rectangular blocks, there are square variations of the blocks that measure 8 inches long and 8 inches high. These standardized dimensions for the most common blocks facilitate building construction by providing easy interfacing with other building components.