Concrete Block Calculator: How Many CMU Blocks?
Find the number of concrete masonry units (CMU or cinder blocks) for a wall, after subtracting doors and windows and adding a waste allowance.
A standard 8×8×16 inch concrete block covers 0.889 sq ft of wall, so you need 1.125 blocks per square foot. A 10 × 10 ft wall needs about 113 blocks, or about 119 with 5% waste. Count corners, caps and lintels separately.
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How to calculate concrete blocks for a wall
A standard 8 × 8 × 16 inch concrete block is described by its nominal size, which includes the mortar joint. The actual block is 3/8 inch smaller in each direction, so the visible face of a laid block is 16 × 8 inches — exactly 0.889 square feet, or 1.125 blocks per square foot.
Blocks needed for common walls (8×8×16, no openings, before waste)
| Wall size | Area | Blocks | Courses |
|---|---|---|---|
| 10 × 4 ft | 40 sq ft | 45 | 6 |
| 20 × 4 ft | 80 sq ft | 90 | 6 |
| 20 × 6 ft | 120 sq ft | 135 | 9 |
| 30 × 6 ft | 180 sq ft | 203 | 9 |
| 40 × 8 ft | 320 sq ft | 360 | 12 |
| 50 × 8 ft | 400 sq ft | 450 | 12 |
| 100 × 6 ft | 600 sq ft | 675 | 9 |
Waste
Five percent is usually enough for straight walls; use 10% for walls with many cuts around openings, or if you are new to masonry. Blocks are delivered by pallet, so round up to full pallets where practical.
Block sizes, weights and fill
| Nominal size (W × H × L) | Typical weight | Common use |
|---|---|---|
| 4 × 8 × 16 in | about 20–25 lb | Non-bearing partitions, veneer backing |
| 6 × 8 × 16 in | about 28–32 lb | Garden and interior walls |
| 8 × 8 × 16 in | about 35–40 lb | Foundations, load-bearing walls |
| 12 × 8 × 16 in | about 50–55 lb | Tall or heavily loaded walls |
Hollow cores can be filled with grout and rebar to make a reinforced wall. Fill only the cores that hold rebar for most walls, and ask your engineer or building department for the spacing. A block wall without a proper footing will crack, however well it is laid.
Special shapes and reinforcement
Corners, bond beams, lintels, half blocks and caps are separate shapes counted by position, not by waste. Load-bearing and retaining walls need vertical rebar and grout-filled cores, plus a footing at least twice the wall thickness — size the footing with the concrete calculator.
Don't forget
- Footing and stem wall per local code.
- Mortar, ties, flashing and weep holes.
- Control joints every 20–25 ft in long walls.
Building a veneer instead? Use the brick calculator; for a garden wall that holds soil, the retaining wall calculator.
Frequently asked questions
How many concrete blocks per square foot?
A standard 8×8×16 in block covers 0.889 sq ft of wall, so you need 1.125 blocks per square foot.
How many cinder blocks do I need for a 10×10 wall?
A 10 × 10 ft wall is 100 sq ft, which needs 113 standard blocks before waste — about 119 with 5% waste.
How many blocks in a pallet?
A full pallet usually holds 72–120 blocks depending on block size and manufacturer. Ask your supplier for the exact count.
How many courses of block for a 6-foot wall?
With 8-inch-tall blocks (nominal), a 6-foot wall needs 9 courses (72 ÷ 8).
How many blocks do I need for a retaining wall?
Use the same formula for the face area; also count cap blocks and any reinforcement or drainage requirements. See the retaining wall calculator for segmental systems.
What is the difference between cinder block and concrete block?
Cinder blocks were made with coal cinders; modern concrete masonry units (CMU) use cement and aggregate, are stronger and heavier, but people still call them cinder blocks.
Do I need to account for corners?
Corner blocks replace standard blocks, so you don't normally add extra — but order the specialty shapes by count rather than relying on waste.
How much does a concrete block cost?
Standard 8×8×16 blocks commonly sell for about $1.50–$4 each, with specialty shapes costing more.
Sources and further reading
- National Concrete Masonry Association — NCMA: concrete masonry resources
- Silica, crystalline (cutting concrete, block, brick and stone) — U.S. Occupational Safety and Health Administration
These references support the general guidance on this page. The calculator applies the standard formulas shown above to the numbers you enter.
Related calculators
. Estimates only. Always confirm quantities with your supplier or a qualified contractor before ordering, and add extra for waste and site conditions.