Concrete Block Calculator: How Many Blocks for a Wall
A wall 20 ft long and 4 ft high needs 95 blocks of the standard 8×8×16 in size, with 5% extra for breakage.
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95 blocks
- Wall area
- 80 sq ft
- Blocks (no breakage)
- 90
- Blocks + 5% breakage
- 95
Key takeaways
- 1.125 standard blocks per sq ft of wall.
- Add 5% for breakage (site rule).
- Standard block: 16×8×8 in nominal.
- A 10×12 shed perimeter, 2 courses ≈ 66 blocks.
How Many Concrete Blocks Do I Need?
You need 1.125 standard blocks per square foot of wall, plus extra for breakage. An 8×16 in nominal block covers 128 sq in, so 144 ÷ 128 = 1.125 blocks fill a square foot. A 20×4 ft wall is 80 sq ft, which is 90 blocks, or 95 blocks with 5% extra (this calculator's own breakage rule).
Concrete Block Formula
Blocks = (Wall length × height − openings) × 1.125 × (1 + breakage %)Blocks for Common Wall Sizes
| Wall | Area | Blocks with 5% extra |
|---|---|---|
| 10×4 ft | 40 sq ft | 48 blocks |
| 20×4 ft | 80 sq ft | 95 blocks |
| 40×4 ft | 160 sq ft | 189 blocks |
| 40×8 ft | 320 sq ft | 378 blocks |
| 100×3 ft | 300 sq ft | 355 blocks |
Concrete Block Size
A standard concrete block is 16×8×8 in nominal, and its actual size is 3/8 in smaller to leave room for the mortar joint, according to common references (Wikipedia, "Concrete block"). The nominal size is what the 1.125 blocks per square foot uses.
Blocks for a Shed Foundation
A perimeter block foundation needs the perimeter length × the number of courses × 0.75 blocks per linear foot (one 16 in block per 1.33 ft). A 10×12 ft shed has a 44 ft perimeter; two courses take about 66 blocks before breakage.
Mortar and Core Fill
Mortar and core-fill amounts depend on the product, so use the coverage printed on the mortar or grout bag; this calculator counts blocks only.
Worked Examples: Blocks for Three Walls
Garden wall 30×3 ft. 90 sq ft × 1.125 = 101.25; with 5%, 107 blocks.
Garage wall 24×8 ft with a 9×7 ft door. (192 − 63) × 1.125 = 145; with 5%, 153 blocks.
Basement wall 40×8 ft. 320 × 1.125 = 360; with 5%, 378 blocks.
How Many Blocks on a Pallet?
Pallet counts vary by supplier and block size, so ask your yard; this site has no primary source for a standard count.
Block Wall Footing
A block wall sits on a concrete footing at least 12 in wide and 6 in deep under the 2021 IRC (R403.1.1); size the concrete with the footing calculator.
How Many Blocks per Square Meter?
About 12.1 standard 16×8 in blocks per square meter (1.125 per sq ft × 10.76).
Concrete Block Weight
Block weight depends on the unit and the maker, so check the yard's spec sheet; this site has no primary source for a standard block weight. For the footing under the wall, concrete weighs about 150 lb/ft³ (this calculator's density).
How Many Concrete Blocks per Square Foot?
1.125 standard 16×8 in blocks cover one square foot of wall face, because each block covers 128 sq in (nominal) and a square foot is 144 sq in.
Concrete Blocks for a Shed Foundation, Step by Step
- Measure the shed's perimeter in feet.
- Multiply by 0.75 blocks per linear foot.
- Multiply by the number of courses.
- Add 5% for breakage.
Concrete Block Calculator FAQ
How many concrete blocks do I need for a 10×12 shed?
A 10×12 ft shed perimeter (44 ft) at two courses needs about 66 blocks before breakage, or 70 with 5% extra.
How do I calculate the number of blocks for my wall?
Multiply wall area in sq ft (minus openings) by 1.125 and add 5% for breakage.
How many concrete blocks for an 8×8 shed foundation?
An 8×8 ft perimeter (32 ft) at two courses needs about 48 blocks before breakage, or 51 with 5% extra.
How many blocks can be laid in a day?
That depends on the mason and the wall; this site does not give labor rates.
Next step
Size the footing with the concrete footing calculator; for walls holding soil, see the retaining wall concrete calculator.
Official sources
Last reviewed 2026-11-05. Numbers come from our tested engine; see how we calculate and our sources.