How many blocks per square foot?
"Cinder block" is the everyday name for a concrete masonry unit (CMU). The standard block is sold as 8 × 8 × 16 inches, but those are nominal sizes: the block itself is 3/8 inch smaller in each direction (7-5/8 × 7-5/8 × 15-5/8 in) so that, with a 3/8 inch mortar joint, each block covers exactly 8 × 16 inches of wall. That is 128 square inches, so one square foot (144 sq in) of wall takes 144 ÷ 128 = 1.125 blocks.
Wall area = length × height − openings
Blocks = wall area (sq ft) × 144 ÷ (nominal face width × height in inches)
Standard 8 × 16 block: blocks = area × 1.125
Blocks per square foot by size
| Nominal face | Face area | Blocks per sq ft | Blocks per 100 sq ft |
|---|---|---|---|
| 8 × 16 in (standard) | 128 sq in | 1.125 | 112.5 |
| 4 × 16 in (half-high) | 64 sq in | 2.25 | 225 |
| 8 × 8 in (half block) | 64 sq in | 2.25 | 225 |
The wall thickness (4, 6, 8, 10 or 12 in) does not change the count, because every common thickness shares the same 8 × 16 face. It does change the weight, the price and how much grout fills the cores.
Worked example 1: a 40 ft garden wall, 4 ft high
- Area = 40 × 4 = 160 sq ft.
- Blocks = 160 × 1.125 = 180 blocks: 6 courses (4 ft ÷ 8 in) of 30 blocks (40 ft ÷ 16 in).
- With 5% waste: 180 × 1.05 = 189 blocks.
Worked example 2: a 24 × 8 ft wall with a door
- Gross area = 24 × 8 = 192 sq ft; a 3 × 7 ft door opening is 21 sq ft, leaving 171 sq ft.
- Blocks = 171 × 1.125 = 192.4; with 5% waste = 202 blocks.
- The wall is 12 courses high with 18 blocks per full course.
Planning the courses
Because each standard block covers 8 inches of height and 16 inches of length, walls work out most neatly when their dimensions are multiples of those numbers. A wall length that is a multiple of 8 inches lets every other course start with a half block without cutting, and a height in 8 inch steps avoids a sliver course at the top. Corners use the same blocks overlapped in a running bond; special corner, bond-beam, lintel and cap blocks are counted in place of standard blocks, not in addition to them.
Mortar, grout and reinforcement
Mortar coverage varies with the product, the joint thickness and the mason, so this calculator does not assume a figure: enter the "blocks per bag" from your mortar bag's coverage chart to get a bag count. Retaining walls and load-bearing walls usually need steel reinforcement and grout-filled cores to the engineer's or code's requirements, which you can estimate separately with the concrete calculator.
How much waste to allow
- 5% covers breakage and a few cuts on a simple straight wall.
- 10% suits walls with many openings, corners or pilasters, or blocks that will be cut on site.
- Leftover blocks are useful for repairs; check whether the supplier accepts returns of full pallets.
Common mistakes
- Using the actual block size (15-5/8 × 7-5/8 in) instead of the nominal size. The joint makes up the difference.
- Forgetting the footing. Block walls sit on a concrete footing, which needs its own concrete order.
- Subtracting openings twice or forgetting that lintels sit over them.
- Building tall retaining walls without design. Walls retaining soil above about 4 ft often need engineering and a permit; check local rules.
Frequently asked questions
How many cinder blocks do I need for a 10 × 10 wall?
A 10 × 10 ft wall is 100 sq ft. Standard 8 × 16 in blocks cover 1.125 per sq ft, so you need 112.5, or 119 blocks with 5% waste.
How many cinder blocks are in a square foot?
1.125 standard 8 × 16 in blocks per square foot, because each block plus its mortar joint covers 128 square inches.
What size is a standard cinder block?
Nominally 8 × 8 × 16 in. The actual block is 7-5/8 × 7-5/8 × 15-5/8 in, and the 3/8 in mortar joint brings it up to the nominal size.
Does wall thickness change the number of blocks?
No. 4, 6, 8, 10 and 12 in thick blocks all share the same 8 × 16 in face, so the count is the same; only weight, cost and grout change.
How many blocks are in a course?
Divide the wall length in inches by 16. A 40 ft wall is 480 in, so 30 standard blocks per course.
Sources
- National Concrete Masonry Association (NCMA), TEK 2-1 Typical Sizes and Shapes of Concrete Masonry Units: nominal vs specified dimensions, 3/8 in mortar joints.
- ASTM C90, Standard Specification for Loadbearing Concrete Masonry Units.
Last reviewed 31 October 2026. Results are estimates; see our disclaimer.