Concrete Block Calculator
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A standard 8 × 8 × 16 in block takes up 8 × 16 = 128 sq in of wall with its mortar joint, so a wall needs 1.125 blocks per square foot. A 40 ft × 8 ft wall (320 sq ft) needs 360 blocks, or 378 with 5% extra.
| Wall | |
| Wall area | 320 sq ft |
| Openings | 0 sq ft |
| Block area | 320 sq ft |
| Blocks | |
| Blocks per sq ft | 1.125 |
| Blocks with no waste | 360 |
| Blocks to buy | 378 |
| Courses (rows) high | 12 |
| Mortar | |
| 80 lb bags of mortar mix (about 30 blocks each) | 12 |
Show steps
- Wall area = 40 × 8 − 0 = 320 sq ft.
- Each block covers 8 × 16 = 128 sq in, so 144 ÷ 128 = 1.125 blocks per sq ft.
- Blocks = 320 × 1.125 = 360; add 5% and round up: 378.
How to use the calculator
- Enter the wall length and height and the area of any openings.
- Choose the block size. Nominal sizes include the ⅜ in mortar joint: an “8 × 8 × 16” block is really 7⅝ × 7⅝ × 15⅝ in.
- Add extra for cuts, then press Calculate.
Blocks per square foot
Blocks per sq ft = 144 ÷ (nominal height × nominal length), in inches.
| Block face | Per sq ft | Per 100 sq ft |
|---|---|---|
| 8 × 16 in | 1.125 | 112.5 |
| 4 × 16 in | 2.25 | 225 |
| 8 × 8 in | 2.25 | 225 |
| 12 × 24 in | 0.5 | 50 |
The thickness (6, 8, 10 or 12 in) does not change the count, only the weight and strength.
Worked example
A garage wall is 24 ft long and 10 ft high with a 3 ft × 7 ft door: 240 − 21 = 219 sq ft. 219 × 1.125 = 246.4 blocks. With 5% extra, buy 259 blocks. The wall is 10 × 12 ÷ 8 = 15 courses high.
Concrete block practice questions
Test yourself with 6 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.
Thickness affects strength and weight, not how many blocks cover the face.
Quiz complete
Frequently asked questions
How many concrete blocks do I need?
Multiply the wall area in square feet by 1.125 for standard 8 × 16 blocks, subtract openings first, and add about 5% for cuts and breakage.
How many blocks are in a pallet?
It depends on the size and the supplier; pallets of 8 × 8 × 16 blocks commonly hold around 90 to 108 blocks. Ask your supplier.
How much mortar for concrete blocks?
A rough guide is one 80 lb bag of mortar mix for about 28 to 32 standard blocks. Wider joints, cut blocks and waste use more.
What are the real dimensions of a cinder block?
A nominal 8 × 8 × 16 block measures 7⅝ × 7⅝ × 15⅝ in. The missing ⅜ in is the mortar joint.
Sources
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