Concrete Block Calculator
Estimate concrete, cinder, and CMU block walls with wall dimensions, block size (including standard three-core 8×8×16 units), per-square-foot block count, door and window deductions, mortar, waste, and optional cost in one workflow.
Calculate Your Concrete Blocks
Enter your CMU wall dimensions below. Add multiple walls and deduct door and window openings for an accurate per-square-foot block count.
Wall 1
Block Size
Industry standard is 5–10%. Increase for complex layouts or cuts.
Enable to enter local prices and see estimated cost.
Results
186
169 blocks + 10% waste
160
sq ft
6
0.45 cu ft cement · 1.35 cu ft sand
Everything You Need to Estimate Materials
Built for DIYers and contractors who want accuracy without complexity.
Multi-Wall Calculator
Add multiple walls with different dimensions and get a combined total — no other tool does this.
Door & Window Deductions
Subtract openings from each wall so you only buy exactly what you need.
Mortar & Materials
Get mortar bags, cement, and sand estimates alongside your block count.
Cost Estimation
Enter your local prices and instantly see the total material cost.
Imperial & Metric
Switch between feet/inches and meters/centimeters with one click.
Waste Factor Built In
Adjustable waste allowance (default 10%) so you never run short.
Related Calculators
Use the standard calculator for CMU block walls. Use a dedicated tool when the project needs different materials or formulas.
How to Use This Concrete Block Calculator
Estimating concrete blocks for your project takes just three simple steps. No complex formulas or spreadsheets needed.
Enter Your Wall Dimensions
Input the length and height of each wall in feet or meters. Need multiple walls? Click "Add Another Wall" to calculate them all at once.
Add Door & Window Openings
For each wall, add doors or windows that need to be subtracted. The calculator deducts these openings from the wall area automatically.
Review Your Material List
Instantly see the total number of concrete blocks needed (with waste factor), mortar bags, cement, sand, and optional cost estimation.
How Many Concrete Blocks Do I Need?
The number of concrete blocks required for any wall depends on three core variables: the wall area, the block face area (including mortar joints), and a waste factor to account for cuts and breakage.
The fundamental formula is:
A standard concrete masonry unit (CMU) in the United States measures 8 × 8 × 16 inches (nominal). The actual dimensions are 7⅝ × 7⅝ × 15⅝ inches, but when you add the standard ⅜-inch mortar joint, each block occupies an 8 × 16 inch area on the wall face — which is exactly 0.889 square feet, or 1.125 blocks per square foot.
For a typical 20 × 8 foot wall (160 sq ft):
160 sq ft ÷ 0.889 sq ft per block ≈ 180 blocks
Add 10% waste: 180 × 1.10 = 198 blocks
Always add a waste factor — 5% for simple rectangular walls, and 10–15% for walls with many openings or complex cuts. Running short of blocks mid-project means a separate trip to the supply yard, which can cost more in time and fuel than a few extra blocks.
Standard Concrete Block Sizes
Concrete blocks (also called cinder blocks or CMU blocks) come in several standard sizes. The most common is the 8×8×16 standard block — a hollow three-core (3-cell) unit weighing roughly 35 pounds — used in residential and commercial CMU wall construction. Each standard block covers 0.889 square feet of wall face, or 1.125 blocks per square foot. Here's a reference table of common sizes:
| Size (inches) | Metric Equiv. (mm) | Blocks per Sq Ft | Common Use |
|---|---|---|---|
| 8 × 8 × 16 | 200 × 200 × 400 | 1.125 | Standard walls, foundations |
| 8 × 4 × 16 | 200 × 100 × 400 | 2.25 | Partition walls, garden walls |
| 4 × 8 × 16 | 100 × 200 × 400 | 1.125 | Non-load bearing partitions |
| 12 × 8 × 16 | 300 × 200 × 400 | 1.125 | Heavy-duty retaining walls |
Mortar & Material Estimates
Mortar is the binding material between concrete blocks, and estimating it correctly prevents costly project delays. A standard 60-pound bag of premixed mortar covers approximately 33 standard 8×16 blocks when applied at the standard ⅜-inch joint thickness for both bed (horizontal) and head (vertical) joints.
For a project requiring 200 blocks, you'd need approximately 7 bags of mortar (200 ÷ 33, rounded up). Beyond premixed bags, you can also estimate the raw materials:
- Cement: approximately 0.075 cubic feet per bag
- Sand: approximately 0.225 cubic feet per bag
Our calculator automatically computes mortar, cement, and sand quantities alongside your block count, so you can purchase all materials in a single trip — whether you're building a 200-block garden CMU wall or a 1,000-block foundation.