How to Calculate Concrete Blocks for a Wall
Calculating concrete blocks (CMU — Concrete Masonry Units) is straightforward: divide the wall area by the face area of a single block (including mortar joints), then add waste. A standard 8×8×16 block with ⅜" mortar joints covers approximately 0.89 square feet of wall face.
The Block Calculation Formula
Number of Blocks = Wall Area (sq ft) ÷ Block Face Area (sq ft) + Waste
For standard 8×8×16 blocks, a common shortcut is 1.125 blocks per square foot of wall. For a 20×8 wall (160 sq ft), you'd need approximately 180 blocks plus 5-10% waste.
Concrete Block Sizes and Uses
| Block Size | Price Each | Common Use |
|---|---|---|
| 8×8×16 Standard | $2.00-$3.00 | Most walls, foundations, retaining walls |
| 8×8×8 Half | $1.50-$2.50 | Corners, ends, and bond patterns |
| 4×8×16 Slim | $1.50-$2.25 | Partition walls, non-load-bearing walls |
| 12×8×16 Wide | $3.00-$4.50 | Foundation walls, below-grade walls |
Mortar Requirements
A standard 80-lb bag of Type S mortar sets approximately 12-15 standard blocks depending on joint thickness and the mason's technique. For a wall of 100 blocks, plan on 7-9 bags of mortar. Type S mortar is recommended for below-grade and structural walls; Type N is suitable for above-grade, non-load-bearing walls.
Block Wall Construction Tips
- Start with a dry layout: Lay the first course dry to check spacing and minimize cutting
- Use a string line: Keeps courses level and plumb — the #1 factor in a professional-looking wall
- Stagger joints: Running bond pattern (offset by half) is standard and provides the strongest wall
- Fill cores: Every 4-6 feet, fill cores with grout and insert vertical rebar for structural walls
- Bond beam: Install a bond beam (horizontal rebar + grout-filled course) at the top of every wall
Cost to Build a Concrete Block Wall
Total installed cost for a concrete block wall ranges from $10-$20 per square foot, including materials, mortar, labor, and reinforcement. Material costs are typically 30-40% of the total, with labor accounting for the remainder. An experienced mason can lay 100-150 blocks per day.
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