Masonry Blocks - Dimensions

Concrete Masonry Unit Blocks (CMU) - dimensions and specifications for standard and half blocks.

Standard Blocks

Typical dimensions for standard concrete masonry unit blocks.

Nominal vs Actual Sizes

Standard blocks have a nominal height of 8 inches and length of 16 inches, with varying widths.

Nominal Size (in)Actual Size (in)
4 x 8 x 163-5/8 x 7-5/8 x 15-5/8
6 x 8 x 165-5/8 x 7-5/8 x 15-5/8
8 x 8 x 167-5/8 x 7-5/8 x 15-5/8
10 x 8 x 169-5/8 x 7-5/8 x 15-5/8
12 x 8 x 1611-5/8 x 7-5/8 x 15-5/8

Half Blocks

Half blocks are used for partial course heights and corners. They have a nominal height of 8 inches and length of 8 inches (half the standard length).

Nominal Size (in)Actual Size (in)
4 x 8 x 83-5/8 x 7-5/8 x 7-5/8
6 x 8 x 85-5/8 x 7-5/8 x 7-5/8
8 x 8 x 87-5/8 x 7-5/8 x 7-5/8
12 x 8 x 811-5/8 x 7-5/8 x 7-5/8

Notes

  • Actual sizes account for typical mortar joint spacing (approximately 3/8 inch)
  • The difference between nominal and actual size allows for standard mortar joint thickness
  • Use the complementary tool to calculate the number of masonry units needed for a project