Calculate blocks needed, mortar bags, and estimated cost for any CMU block wall. Includes 10% waste factor.
Accurate block estimation saves trips to the supply yard and prevents costly delays mid-project. Here's how to get it right.
Blocks = (Wall Area in sq ft) × Blocks per sq ft × 1.10 (waste)
Standard 8×8×16 blocks (with 3/8" mortar joints) cover about 0.89 sq ft each, meaning you need 1.125 blocks per square foot.
| Block Size | Actual Dimensions | Blocks per Sq Ft | Cost Each | Weight |
|---|---|---|---|---|
| 8×8×16 (Standard) | 7⅝ × 7⅝ × 15⅝" | 1.125 | $1.50–$3.00 | 35–40 lb |
| 8×4×16 (Half) | 7⅝ × 3⅝ × 15⅝" | 2.25 | $1.25–$2.50 | 22–26 lb |
| 12×8×16 | 11⅝ × 7⅝ × 15⅝" | 1.125 | $2.50–$4.50 | 50–55 lb |
One 80-lb bag of pre-mixed mortar lays approximately:
| Type | Strength (PSI) | Best For |
|---|---|---|
| Type M | 2,500 | Below grade, foundations, retaining walls |
| Type S | 1,800 | Structural walls, chimneys, exterior at grade |
| Type N | 750 | General purpose, above-grade exterior walls |
| Type O | 350 | Interior non-load-bearing walls |
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