What are the actual dimensions of an 8 by 8 by 16 block?

• A. 7 5/8 x 7 5/8 x 15 5/8
• B. 8 x 8 x 16
• C. 7 x 7 x 15
• D. 8 1/2 x 8 1/2 x 16

Answer: (A)

When working with concrete masonry units, think about nominal size versus actual size. The nominal size is the size used for ordering and plans, while the actual size is smaller once you include the mortar joints that will be between blocks.

For a standard CMU block that is nominally 8 by 8 by 16 inches, the typical actual dimensions are 7 5/8 inches by 7 5/8 inches by 15 5/8 inches. The 3/8 inch deduction in each dimension accounts for the mortar joints, which reduces the overall measurements in every direction.

That’s why the actual dimensions are 7 5/8 x 7 5/8 x 15 5/8 inches. The other options reflect the nominal size or nonstandard reductions and don’t match the typical actual size used in masonry work.