Concrete Block (CMU) Sizes
Concrete Masonry Units (CMU), or Concrete Blocks, come in a variety of sizes. CMUs are identified by their depth. 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.
4" CMU
Actual Size | Nominal Size |
| 3 7/8 x 7 5/8 x 7 5/8 | 4 x 8 x 8 |
| 3 7/8 x 7 5/8 x 15 7/8 | 4 x 8 x 16 |
6" CMU
Actual Size | Nominal Size |
| 5 7/8 x 7 5/8 x 7 5/8 | 6 x 8 x 8 |
| 5 7/8 x 7 5/8 x 15 7/8 | 6 x 8 x 16 |
8" CMU
Actual Size | Nominal Size |
| 7 7/8 x 7 5/8 x 7 5/8 | 8 x 8 x 8 |
| 7 7/8 x 7 5/8 x 15 7/8 | 8 x 8 x 16 |
10" CMU
Actual Size | Nominal Size |
| 9 7/8 x 7 5/8 x 7 5/8 | 10 x 8 x 8 |
| 9 7/8 x 7 5/8 x 15 7/8 | 10 x 8 x 16 |
12" CMU
Actual Size | Nominal Size |
| 11 7/8 x 7 5/8 x 7 5/8 | 12 x 8 x 8 |
| 11 7/8 x 7 5/8 x 15 7/8 | 12 x 8 x 16 |
2004 CSI Masterspec Division
Concrete Unit Masonry: 04 22 00
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