Concrete Masonry Units (CMU), or Concrete Blocks, come in a variety of sizes.  CMUs are identified by their depth - i.e. the thickness of the wall they create.  For instance, a 6" CMU is nominally 6" deep.  As with brick, CMUs have actual dimensions and nominal dimensions.  The nominal dimension of a CMU is the actual dimension plus the width of the mortar joint.  Typical CMU mortar joints are 3/8".  The nominal dimension works within the 4" grid that other construction materials follow.

Nominal Dimensions of an 8" CMU   Actual Dimensions of an 8" CMU

4" CMU

Actual Size
D x H x L (inches)
Nominal Size
D x H x L (inches)
3 5/8 x 7 5/8 x 7 5/84 x 8 x 8
3 5/8 x 7 5/8 x 15 5/84 x 8 x 16

6" CMU

Actual Size
D x H x L (inches)
Nominal Size
D x H x L (inches)
5 5/8 x 7 5/8 x 7 5/86 x 8 x 8
5 5/8 x 7 5/8 x 15 5/86 x 8 x 16

8" CMU

Actual Size
D x H x L (inches)
Nominal Size
D x H x L (inches)
7 5/8 x 7 5/8 x 7 5/88 x 8 x 8
7 5/8 x 7 5/8 x 15 5/88 x 8 x 16
Ad - Article Continues Below

10" CMU

Actual Size
D x H x L (inches)
Nominal Size
D x H x L (inches)
9 5/8 x 7 5/8 x 7 5/810 x 8 x 8
9 5/8 x 7 5/8 x 15 5/810 x 8 x 16

12" CMU

Actual Size
D x H x L (inches)
Nominal Size
D x H x L (inches)
11 5/8 x 7 5/8 x 7 5/812 x 8 x 8
11 5/8 x 7 5/8 x 15 5/812 x 8 x 16
Ad - Article Continues Below

Masonry Manufacturers

Masonry and Related Products

Help make archtoolbox better. If you found an error or out of date information in this article, please let us know.

Archtoolbox Monthly Newsletter: Website updates, industry news, career growth, and more. Sign up now!