Understanding Concrete Masonry Units (CMUs)
The **Concrete Masonry Unit (CMU)**, commonly called a cinder block or concrete block, is a critical component in construction. This calculator uses the standard size, which is nominally **8 inches high by 16 inches long** (with an actual size of $7\frac{5}{8}" \text{ by } 15\frac{5}{8}"$ to accommodate a $3/8"$ mortar joint).
Calculation and Coverage
The industry standard for estimating is based on the area covered by one block *including* the mortar joint. $$\text{Blocks Required (Raw)} = \text{Wall Area (sq. ft.)} \times 1.125$$ $$\text{Blocks to Order} = \lceil \text{Raw Blocks} \times (1 + \text{Waste Factor}) \rceil$$ The constant **1.125 blocks per square foot** accounts for the nominal 8"x16" coverage. All final counts are rounded up ($\lceil \dots \rceil$) to ensure material sufficiency.
Mortar and Waste Considerations
Mortar Mix Estimate
- **CMU Mortar Type:** Type N mortar is most common for non-structural and above-grade applications.
- **Coverage:** A single 80 lb bag of pre-mixed mortar is typically sufficient for laying **40 to 50** standard CMUs.
- **Order Requirement:** Always round the mortar bag count up, as consistency and job-site conditions can affect usage.
Adjusting for Openings
- **Doors/Windows:** The calculator provides a total wall estimate. For accuracy, subtract the square footage of any door or window openings before calculating.
- **Lintels:** You will also need to calculate and purchase steel or concrete **lintels** (or bond beams) to span the top of any opening.
Essential Tip for CMU Construction:
Unlike wood framing, concrete block walls require specialized corner, half-blocks, and bond beam blocks. While this calculator provides the total quantity, consult your supplier to ensure you get the correct ratio of **"specials"** (corners, sills, etc.) based on your wall plan.