Concrete Block Calculator
Block count for a wall from its length and height. Standard CMU is 8″ high × 16″ long nominal — the ⅜″ mortar joint is already in that number, so it is 1.125 blocks per square foot. Half-high and segmental retaining-wall units are in the size list.
Order 378 blocks (5 cubes) — block ships in cubes of 90; corner and half blocks are ordered separately.
- Area
- 320 ft²
- Unit 8×16″
- 1.13 per ft²
- Net blocks
- 360
- Waste / cuts 5%
- + 18
- Blocks to buy
- 378
- Cubes90 per cube
- 5
- Mortar, 80 lb bags (type N/S)
- 31 bags
- Mason sand, 50 lb bags
- 72 bags
- Materials + delivery$2–$4 / block · Sep 2026
- $881 – $1,637
- Installed (with labor)typ. $5,005
- $3,441 – $8,037
Quantities follow the ticket. Links may earn us a commission at no cost to you; they never change a number.
What will this block (cmu) job cost?
See the installed price range for these quantities and get up to 3 quotes from local contractors. Free, no obligation.
How to calculate concrete block by hand
Blocks = Wall area (ft²) × 1.125 × (1 + waste) · Mortar bags = blocks ÷ 12.5
Worked example
- Wall area: 40 ft × 8 ft = 320 ft².
- Standard block face 8 × 16″ nominal = 0.889 ft² → 1.125 blocks per ft².
- Net: 320 × 1.125 = 360 blocks; with 5% waste, 378 → order 5 cubes (90 each) or 378 loose.
- Mortar: 378 ÷ 12.5 ≈ 31 × 80 lb bags; mason sand about 1 yd³ per 7 bags if mixing from bulk.
- Standard 8 × 8 × 16 block
- 1.125 per ft² · 37 lb
- Mortar per 100 block
- ≈ 8 × 80 lb bags
- Cube of block
- 90 pcs · ≈ 3,300 lb
- Courses per 8 ft wall
- 12
Questions crews ask
How many concrete blocks do I need?
Wall length × height in feet gives square feet; multiply by 1.125 for standard 8 × 16″ block and add 5% for waste. A 40 × 8 ft wall is 320 ft² → 360 blocks, order 378. Corners need corner blocks and every other course needs half blocks — order those separately.
How much mortar for 100 blocks?
About 8 × 80 lb bags of type N or S mortar per 100 standard blocks with ⅜″ joints (12–13 blocks per bag). From bulk, one bag of masonry cement plus 2¼–3 parts sand lays 25–35 blocks.
How many blocks are in a cube?
90 standard 8 × 8 × 16 blocks, weighing about 3,300 lb. Lightweight block cubes run 96; 12″ block cubes 60. Yards charge a per-cube delivery fee, so round to whole cubes and keep the extras.
How many blocks per course?
Divide the wall length in inches by 16. A 40 ft (480″) wall takes 30 blocks per course; an 8 ft wall is 12 courses. Running bond needs a half block at the start of every other course.
Do I need to fill the block cores?
Foundation and retaining walls: yes, at least the cores with vertical rebar, per code (often every 32–48″ plus corners and ends). Filling every core takes about 0.5 ft³ of grout per standard block — 45 blocks per cubic yard.