CMU Block Calculator
Enter your wall's length and height to find how many standard concrete masonry units (CMUs) you need, with mortar and a course count.
A standard CMU (concrete masonry unit) has a nominal face of 16 inches long by 8 inches high — including the mortar joint — so each block covers about 0.89 square feet of wall. That works out to roughly 1.125 blocks per square foot, the figure this calculator uses.
How to calculate CMU blocks
Find the wall area (length × height), multiply by 1.125 blocks per square foot, then add a waste allowance for cuts and breakage.
Blocks = Wall area × 1.125
Order = Blocks × (1 + waste %)
| Item | Value used |
|---|---|
| Nominal block face | 16 in × 8 in (with joint) |
| Blocks per sq ft | 1.125 |
| Course height | 8 in (so 1.5 courses per foot of height) |
| Mortar | ≈ 1 bag per ~35 blocks (3/8 in joints) |
Worked example
A wall 20 ft long and 8 ft high:
| Area = 20 × 8 | 160 sq ft |
| Blocks = 160 × 1.125 | 180 |
| With 5% waste | 189 |
| Courses = 8 ft ÷ 8 in | 12 high |
CMU vs cinder block
"CMU" and "cinder block" are often used interchangeably, and the sizing is identical, so this calculator and our cinder block calculator use the same block-per-square-foot figure. The technical difference is the aggregate: modern CMUs use concrete aggregate, while traditional cinder blocks used coal cinders and are rarely made today.