How to use the concrete block calculator
- Enter the wall length and height.
- Choose the block size and confirm the mortar joint thickness.
- Subtract the area of any openings, add a waste allowance, and optionally a price per block.
How the calculation works
Concrete masonry units are made slightly smaller than their nominal size so that, with a mortar joint, they fill a modular grid. A standard block measures 15⅝ × 7⅝ in on its face; with a ⅜ in joint it occupies exactly 16 × 8 in: 128 sq in, or 1.125 blocks per square foot.
The calculator rounds the number of courses (rows) and blocks per course up, so partial blocks at the ends and top are counted as whole blocks. Openings are subtracted in whole blocks, then the waste allowance is added.
Formula
- L, H
- Wall length and height
- l, h
- Actual block length and height
- j
- Mortar joint thickness
Worked example
40 ft × 4 ft wall of 8 × 8 × 16 block
Courses = 48 ÷ 8 = 6. Per course = 480 ÷ 16 = 30. Blocks = 180; with 5% waste 189 blocks. (Check: 160 sq ft × 1.125 = 180.)
Assumptions and limitations
- Mortar, grout, reinforcement and special units (corner, bond beam, lintel, cap) are not calculated.
- Wall design (footing size, reinforcement, grouting and height limits) must follow your building code or an engineer.
Frequently asked questions
How many concrete blocks are in a square foot?
For standard 8 × 16 in (nominal) block, 1.125 blocks per square foot, or 112.5 blocks per 100 sq ft.
What are the actual dimensions of an 8 × 8 × 16 block?
Typically 7⅝ × 7⅝ × 15⅝ in. The ⅜ in mortar joint brings it to the 8 × 8 × 16 in nominal size.
How do I estimate blocks for a wall with a door or window?
Enter the total area of the openings in square feet. The calculator removes only the whole blocks that fit inside the openings, then adds your waste allowance. Openings also need lintels or bond-beam blocks above them, which you should count separately.
Does block width (4, 6, 8, 12 in) change the count?
No. The face size is the same, so the number of blocks per square foot is the same. Width affects weight, cost and structural capacity.