Quick answer: A wall built with standard 8 × 8 × 16 inch concrete blocks needs 1.125 blocks per square foot (112.5 per 100 sq ft). Multiply the wall length by its height, multiply by 1.125, then add 5–10% for breakage and cuts.
Whether you are building a garden wall, a raised bed, a retaining wall or a shed foundation, counting blocks correctly saves money and trips to the supplier. There are two easy ways to do it: by area and by courses. Both give the same answer.
Method 1: By Wall Area
A standard concrete masonry unit (CMU) is actually 7⅝ × 15⅝ inches on its face. With a ⅜ inch mortar joint, each block covers a nominal 8 × 16 inches, which is 0.889 square feet.
Blocks = Wall length (ft) × Wall height (ft) × 1.125
Example: a wall 20 ft long and 6 ft high is 120 sq ft. 120 × 1.125 = 135 blocks. With 5% extra, order 142 blocks.
Method 2: By Courses
Each block is 16 inches long, so a course (row) needs 0.75 blocks per foot of wall. Each course is 8 inches high, so a wall needs 1.5 courses per foot of height.
- Blocks per course = Wall length (ft) × 12 ÷ 16
- Number of courses = Wall height (in) ÷ 8
- Total blocks = Blocks per course × Courses
Example: a 30 ft wall that is 4 ft high needs 30 × 12 ÷ 16 = 22.5 blocks per course and 48 ÷ 8 = 6 courses, so 135 blocks. Counting by courses is useful because it shows where you will need half blocks at the ends of alternate courses.
Skip the math: enter the wall size and openings and choose US blocks, US bricks or UK/EU blocks and bricks. Open the free Block & Brick Calculator →
Blocks and Bricks per Square Foot and Square Meter
| Unit | Per sq ft | Per m² |
|---|---|---|
| US concrete block (8×8×16 in) | 1.125 | ≈12.1 |
| US modular brick | 6.75 | ≈72.7 |
| UK/EU block (440×215 mm) | ≈0.92 | ≈10 |
| UK/EU brick (215×65 mm) | ≈5.5 | ≈60 |
Subtract Doors and Windows
Work out the area of each opening (width × height) and subtract it from the wall area before you multiply. A standard 3 × 7 ft door opening is 21 sq ft, which saves about 24 blocks.
How Much Mortar?
A common rule of thumb for US block walls is about 8.5 cubic feet of mortar per 100 blocks, which is roughly 13 bags of 80 lb pre-mixed mortar mix, or about 3 bags of masonry cement mixed on site with sand. In the UK, allow about 1 m³ of mortar per 1,000 blocks and about 0.5 m³ per 1,000 bricks. Joint size and bond pattern change these figures, so buy a little extra.
Don’t Forget
- Corner blocks, bond beam blocks and cap blocks are ordered separately.
- Block walls need a solid concrete footing. Our concrete calculator sizes it.
- Retaining walls and walls over about 4 ft (1.2 m) often need engineering, rebar and a permit.
- Order 5% extra for straight walls and up to 10% for walls with many openings.
Frequently Asked Questions
How many blocks are in 100 square feet?
About 113 standard 8×8×16 inch blocks, or 118 with 5% extra for breakage.
How many blocks are in a course?
Each block is 16 inches long, so a course needs three blocks for every 4 feet of wall, or 0.75 blocks per foot.
How many bricks are in a square meter?
About 60 standard UK/EU bricks for a single-skin wall with 10 mm mortar joints.
Related Guides
- How Many Bags of Concrete Do I Need? (10×10 Slab and More)
- How Much Gravel Do I Need for a Driveway?
- How Much Mulch Do I Need? Bags, Yards and Coverage
Try the free Concrete Block & Brick Calculator or browse all home improvement calculators.