Concrete Block (CMU) Calculator
Number of 8×8×16 concrete blocks (CMU) for a wall. A standard block plus a ⅜ in joint covers 16 × 8 in, so about 1.125 blocks per square foot.
Formula
Blocks per sq ft = 144 ÷ ((length + joint) × (height + joint)) = 144 ÷ (16 × 8) = 1.125 for standard units; blocks = net wall area × 1.125 × (1 + waste%).
Worked example
Inputs: Wall length = 40 ft; Wall height = 8 ft; Openings to subtract = 0 sq ft; Block length (actual) = 15.625 in; Block height (actual) = 7.625 in; Mortar joint = 0.375 in; Waste allowance = 5 %.
| Wall area sq ft | 320 |
|---|---|
| Units per sq ft | 1.125 |
| Units | 378 |
FAQ
How many blocks are in a 10 ft by 8 ft wall?
80 sq ft × 1.125 = 90 blocks before waste.
Does this include grout, rebar or bond beams?
No. It counts units only; reinforcement and grout are set by your structural drawings.
Sources
- NCMA: Concrete Masonry Unit Shapes, Sizes, Properties and Specifications (nominal 8×8×16 in units are 7⅝×7⅝×15⅝ in actual)
- Geometry (volume/area formulas); no external constant needed
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Last reviewed 2026-10-13.