Concrete Block Sizes and CMU Dimensions

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 5/8
 4 x 8 x 8
 3 5/8 x 7 5/8 x 15 5/8
 4 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 5/8
 6 x 8 x 8
 5 5/8 x 7 5/8 x 15 5/8
 6 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 5/8
 8 x 8 x 8
 7 5/8 x 7 5/8 x 15 5/8
 8 x 8 x 16

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 5/8
 10 x 8 x 8
 9 5/8 x 7 5/8 x 15 5/8
 10 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 5/8
 12 x 8 x 8
 11 5/8 x 7 5/8 x 15 5/8
 12 x 8 x 16

2004 CSI Masterspec Division

Concrete Unit Masonry: 04 22 00


 


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