The Block CalculatorWhat is a CMU?
A concrete masonry unit (CMU) is a standard-size precast block made from Portland cement, aggregate and water. CMUs come hollow or solid and are named by nominal width: 4″, 6″, 8″, 10″ and 12″. The 8″ × 8″ × 16″ unit is the most common in North America.
How does this CMU block calculator work?
Enter the wall size and the nominal CMU face size (length × height). The calculator divides the areas and rounds up. Nominal width does not affect the count, but it does affect weight, grout volume and cost, so use it when you pick a unit.
Formula used
Total Blocks = (Wall Length × Wall Height) ÷ (Block Length × Block Height)The result is always rounded up to the next whole CMU, because you can’t buy part of one. Wall thickness is shown in the diagram but does not change the count for a single-wythe wall.
Example
Scenario: A wall 10 m long and 2 m high using CMUs with a 40 × 20 cm face.
Wall area: 10 × 2 = 20 m²
CMU face area: 0.4 × 0.2 = 0.08 m²
Final result: 20 ÷ 0.08 = 250 CMUs.
Frequently asked questions
What does nominal size mean for a CMU?
The nominal size includes a ⅜″ mortar joint. An 8 × 8 × 16 CMU actually measures 7⅝ × 7⅝ × 15⅝ inches.
How many CMUs per square foot?
With 8″ × 16″ units, 1.125 CMUs per square foot of wall.
Last updated: . Results are estimates — see our disclaimer.