Wall area — sq ft | waste —% included
Material Shopping List
- CMU block—
- Mortar—
- Vertical rebar—
- Horizontal rebar—
- Block cost—
- Mortar + rebar cost—
- Estimated material cost—
Block Coverage Chart
| Block size | Face coverage | Blocks per 100 sq ft |
|---|---|---|
| 8x8x16 CMU | ~0.89 sq ft | ~113 |
| 6x8x16 CMU | ~0.89 sq ft | ~113 |
| 12x8x16 CMU | ~0.89 sq ft | ~113 |
All standard CMU share a 16 x 8 in face, so coverage is the same; only the width (and price) changes.
Mortar Consumption Guide
| Blocks | Mortar (approx.) |
|---|---|
| 100 blocks | ~0.33 cu yd (about 8 to 9 bags) |
| 300 blocks | ~1 cu yd |
| 600 blocks | ~2 cu yd |
Roughly one cubic yard of mortar lays 300 standard blocks with 3/8 in joints.
How Many Blocks Do I Need for a Wall?
Concrete block is estimated from the wall area. A standard CMU has a 16 by 8 inch face, which covers about 0.89 square feet, so a wall needs roughly 1.125 blocks per square foot. Find the wall area by multiplying length times height, subtract any door, window, or gate openings, add a waste factor, and multiply by 1.125. This calculator does that and then estimates the mortar, vertical and horizontal rebar, and total cost, turning a block count into a complete material shopping list instead of a single number.
Mortar and Rebar for a Block Wall
Beyond the block itself, a real wall needs mortar and usually steel. As a rule of thumb, one cubic yard of mortar lays about 300 standard blocks with three-eighths inch joints, so a 400 block wall takes a bit over a cubic yard. Reinforcement depends on the job: a light garden wall might use vertical bars every four feet, while a retaining or foundation wall is reinforced far more heavily, often every 16 to 24 inches both ways with grouted cells. Set the spacing to match your wall and the calculator returns vertical bar count and horizontal linear feet.
Block Wall Types
The same block builds very different walls. A garden or privacy wall is mostly cosmetic and lightly reinforced. A retaining wall resists soil and water and needs drainage, a solid base, and engineering for anything tall. Foundation and basement walls carry structural loads and resist backfill pressure, so they are grouted and reinforced to an engineered spec on a poured footing. Structural CMU walls in buildings follow the same logic. Picking the wall type here sets sensible default reinforcement and flags when you should involve an engineer.
Frequently Asked Questions
How many blocks per square foot? About 1.125 standard blocks per square foot of wall, or roughly 113 blocks per 100 square feet.
How much mortar per block? Around one cubic yard, or 8 to 9 bags, per 300 blocks.
Do I need rebar in a block wall? Light freestanding walls may not, but retaining, foundation, and structural walls require reinforced and grouted cells per code.
What waste factor should I use? 5 percent simple, 10 percent normal, 15 percent for complex walls with many cuts.