How Many Concrete Blocks Do I Need? (CMU Wall Calculator + Chart)
Part of Concrete & Masonry
Quick answer
Multiply the wall's length by its height in feet to get the area, then multiply by 1.125 for standard 8×8×16 blocks. A 20 × 8 ft wall (160 ft²) needs about 180 blocks, or 198 with 10% waste. Subtract any door and window openings first.
Concrete blocks — CMU, cinder block, breeze block, whatever you call them — are counted from the wall's face area, not its volume. A standard block lays up 8 inches tall and 16 inches long, so it covers a known slice of wall and you simply work out how many of those slices fit.
The formula
Blocks = (length ft × height ft − openings) × blocks per ft² × (1 + waste)
A standard 8×8×16 block with a 3/8-inch mortar joint covers about 0.889 ft² of wall (16 × 8 inches plus the joints). One block per 0.889 ft² works out to 1.125 blocks per square foot — the figure every block yard and mason uses, from NCMA's TEK guidance.
Blocks per square foot by size
| Block (nominal) | Face size | Blocks per ft² | Typical use |
|---|---|---|---|
| Standard 8×8×16" | 16 × 8 in | 1.125 | Most walls, foundations, stem walls |
| 4" (4×8×16) | 16 × 8 in | 1.125 | Veneer, partition walls |
| 6" (6×8×16) | 16 × 8 in | 1.125 | Light walls, partitions |
| 12" (12×8×16) | 16 × 8 in | 1.125 | Tall / load-bearing / foundation walls |
| Half-height 8×8×8" | 8 × 8 in | 2.25 | Coursing fill, short returns |
Notice the width (4, 6, 8, 10, 12 inch) doesn't change the count — every full-height block shares the same 16 × 8-inch face, so it's always 1.125 per square foot. Width only changes the wall thickness, the weight and the price. A half-height block is the exception at 2.25.
Calculate blocks, mortar & fillConcrete Block CalculatorCalculate how many concrete blocks (CMU / cinder blocks) a wall needs, plus the bags of mortar and optional core-fill grout — from the wall's length, height, block size and openings.OpenBlock counts for common walls (standard 8×8×16, +10% waste)
| Wall (L × H) | Area | Blocks (base) | Blocks to order |
|---|---|---|---|
| 10 × 8 ft | 80 ft² | 90 | 99 |
| 20 × 8 ft | 160 ft² | 180 | 198 |
| 30 × 8 ft | 240 ft² | 270 | 297 |
| 40 × 8 ft | 320 ft² | 360 | 396 |
| 50 × 8 ft | 400 ft² | 450 | 495 |
Courses and blocks per course
Each course (row) of standard block adds 8 inches of height with its joint, so courses = wall height in inches ÷ 8. Blocks per course = wall length in inches ÷ 16. An 8-foot wall is 12 courses; a 20-foot run is 15 blocks per course. If the height doesn't divide evenly by 8 inches, the top course gets cut down.
Don't forget the mortar
Plan about 3 bags of 70 lb Type S mortar mix per 100 blocks for standard 3/8-inch joints — so a 198-block wall takes roughly 6 bags. Pre-mixed mortar bags already include the sand. Reinforced and foundation walls also have their cores filled with grout (about a quarter cubic foot per standard block) and rebar set per local code.
Always add about 10% for cuts at corners and openings and for breakage — suppliers rarely take back cut or chipped block. The calculator does the area, waste rounding, mortar and optional core-fill grout in one shot.
FAQs
How many blocks are in a square foot?
About 1.125 standard 8×8×16 blocks per square foot of wall face. Each block covers roughly 0.889 ft² including its mortar joints. A half-height 8×8×8 block is 2.25 per square foot.
How many concrete blocks do I need for a 100 square foot wall?
About 113 blocks (100 × 1.125), or roughly 119–124 once you add 5–10% for waste. Subtract door and window openings from the 100 ft² before multiplying.
How many blocks do I need for a 10 × 10 ft wall?
A 10 × 10 ft wall is 100 ft², so about 113 standard blocks, or 124 with 10% waste, plus roughly 4 bags of mortar.
Does block width change how many I need?
No. A 4, 6, 8, 10 or 12-inch block all share the same 16 × 8-inch face, so all lay up at 1.125 blocks per square foot. Width changes the wall thickness, weight and price, not the count.