Short answer: A standard 8 by 16 inch concrete block covers 0.89 square feet of wall, so you need about 1.125 blocks per square foot. A wall 20 ft long and 4 ft high needs about 90 blocks, or 95 with 5% extra for breakage.
| Wall size | Wall area | Blocks, no waste | Blocks, 5% extra |
|---|---|---|---|
| 10 x 4 ft | 40 sq ft | 45 | 48 |
| 20 x 4 ft | 80 sq ft | 90 | 95 |
| 20 x 6 ft | 120 sq ft | 135 | 142 |
| 30 x 6 ft | 180 sq ft | 203 | 213 |
| 40 x 8 ft | 320 sq ft | 360 | 378 |
How the count is worked out
A standard concrete block is called 8 by 8 by 16 inches, but the real block is 3/8 inch smaller in each direction so it fits the mortar joint. Each block, with its joint, takes up a face of 16 by 8 inches, which is 128 square inches. A square foot is 144 square inches, so you need 144 divided by 128, or 1.125 blocks per square foot.
You can also count by rows. A course of blocks is 8 inches high, so a wall needs 1.5 courses for every foot of height. Each course needs 0.75 blocks for every foot of length.
Openings, corners and waste
Subtract the area of doors and windows before you multiply. Corners and the ends of walls often need cut blocks or special end blocks, so add 5 percent for cuts and breakage, and a little more for a wall with many corners.
Walls that carry weight or hold back soil usually need reinforcement, such as steel bars in filled cores. Ask a local professional before you build anything structural.
Worked example
A wall 24 ft long and 5 ft high has 120 square feet. At 1.125 blocks per square foot that is 135 blocks. Adding 5% gives 141.75, so order 142 blocks.
Use the Brick and Block CalculatorEnter your own measurements and get an exact amount.
Frequently asked questions
How many blocks are in a square foot?
About 1.125 standard 8 by 16 inch blocks, with the mortar joint included.
How many blocks do I need for a 10 by 10 foot room?
The walls are 40 feet around. At 8 feet high that is 320 square feet, or about 360 blocks, before you take out doors and windows.
How tall is one course of block?
Eight inches, including the mortar joint, so a wall 4 feet high has 6 courses.
Does the calculator count bricks or blocks?
Both. Choose the block size when you enter the wall and it gives the count with your waste allowance.
More quick answers
Related calculators
Figures are typical planning values. Material sizes, densities and local requirements vary, so confirm with your supplier before ordering.
Last updated October 11, 2026.