# 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.

**Quick answer:** 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.

_Last updated: October 3, 2026. Estimates only; confirm quantities with your supplier._

## 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 = (wall length × wall height − openings) ÷ face area per block × (1 + waste %)
```

### 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](../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](../brick-calculator/); for a garden wall that holds soil, the [retaining wall calculator](../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](https://ncma.org/) — NCMA: concrete masonry resources
- [Silica, crystalline (cutting concrete, block, brick and stone)](https://www.osha.gov/silica-crystalline) — U.S. Occupational Safety and Health Administration