How many concrete blocks per square foot?
Standard 8×16 face concrete blocks lay 1.125 per square foot of wall. A 100 square foot wall takes 112.5 blocks, or 119 blocks with the 5% waste allowance CMHA’s estimating guide uses.
How to work it out
- 6 courses of 8 in (block + ⅜ in joint) · 25 ft ÷ 16 in = 19 blocks per course
- 100 sq ft ÷ 0.889 sq ft per block face + 5% = 119 blocks
- Mortar: 113 blocks ÷ 13 per 80 lb bag + 15% (BIA suggests 15–25%) = 10 bags
This is the one number that makes block estimating quick. Measure the wall, multiply by 1.125, add a little for breakage — the rest is details.
Adjust for your project
More options: Openings · Extra
- Courses (rows)
- 6 courses
- Blocks per course (to the next half)
- 19
- Blocks per square foot
- 1.125 per sq ft
- Wall area (net of openings)
- 100 sq ft
- Mortar mix, 80 lb bags (incl. 15% extra)
- 10 bags
- Actual block size
- 7-5/8 × 7-5/8 × 15-5/8 in
- Count corner, end and bond-beam units separately if your wall needs them; ask the supplier which shapes they stock.
Blocks by wall area (4 ft high, 5% extra)
| Wall length | Blocks to buy | Wall area (net of openings) | Mortar mix, 80 lb bags (incl. 15% extra) |
|---|---|---|---|
| 12.5 ft | 60 blocks | 50 sq ft | 5 bags |
| 25 ft | 119 blocks | 100 sq ft | 10 bags |
| 50 ft | 237 blocks | 200 sq ft | 20 bags |
| 100 ft | 473 blocks | 400 sq ft | 40 bags |
Where 1.125 comes from
With its ⅜ in joints, each standard block fills a rectangle 8 in high and 16 in long: 128 square inches, or 8/9 of a square foot. Nine blocks cover eight square feet, so a square foot takes 9/8 = 1.125. It holds for every block thickness — 4, 6, 8, 10 or 12 in — because they share the same face. Half-high blocks (8×4×16) have half the face, so they lay 2.25 per square foot.
CMHA’s TEK 04-02A turns that into 119 units per 100 sq ft with a 5% allowance for waste and breakage. That is the count here: a 25 ft wall 4 ft high is 100 sq ft.
Using it on a real wall
Subtract door and window openings from the area before multiplying. Count special units — corners, ends, lintels, bond beams — separately, since they replace standard blocks in particular places. Mortar follows from the block count: at Quikrete’s 13 blocks per 80 lb bag plus 15% extra, 100 sq ft is about 10 bags. See how many bags of mortar per 100 block and 8×8×16 block actual size.
Different size? Use the full Concrete Block Calculator.
What you’ll need
- Brick trowelBudget price
Spreads and furrows the mortar bed and butters the ends of each block or brick. A 10–11 in trowel suits most hands.
See options on Amazon (opens in a new tab) - Mortar jointerBudget price
Tools mortar joints to a concave finish once they are thumbprint-hard, which compacts them and sheds water.
See options on Amazon (opens in a new tab) - Mason’s line and line blocksBudget price
Bright braided line stretched between line blocks keeps each course of block or brick straight and level, and marks out slab edges.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How many cinder blocks for a 6 foot wall 20 feet long?
142 blocks with 5% extra (9 courses).
How many half-high blocks per 100 square feet?
237 blocks with 5% extra: 2.25 per sq ft.
Other common sizes
- 8×8×16 block actual size — 7-5/8 × 7-5/8 × 15-5/8 in (194 × 194 × 397 mm)
- How many cinder blocks for a 10×10 shed — 89 blocks for a 3-course wall (28 per course)
Sources
- CMHA (formerly NCMA) CMU-TEC-001-23 — Concrete masonry unit shapes, sizes, properties and specifications (opens in a new tab) — Specified dimensions are 3/8 in less than nominal, so an 8×8×16 block is 7-5/8 × 7-5/8 × 15-5/8 in; nominal thicknesses 4–16 in; ±1/8 in tolerance.
- CMHA (formerly NCMA) TEK 04-02A — Estimating concrete masonry materials (opens in a new tab) — Each 8×16 unit covers 8/9 sq ft, so 112.5 units per 100 sq ft (119 with 5% waste); grout per 100 sq ft by unit width and core spacing (Table 3); cores filled per 80 lb grout bag (Table 4); one 80 lb bag of preblended mortar lays about 16 CMU with face-shell bedding (Table 2).
- Quikrete Mortar Mix (No. 1102) data sheet (opens in a new tab) — Each 80 lb bag lays up to 37 standard bricks or 13 standard 8×8×16 blocks.