DIY CalculatorThe default adds 5% for cuts and breakage. Subtract the area of doors and windows by entering the wall in sections.
Good to know
- Standard blocks: 1.125 per square foot of wall.
- Mortar: about 8.5 cubic feet per 100 blocks.
- Retaining walls over 3–4 feet usually need engineering.
- Order bond beam and corner blocks separately.
Blocks needed by wall area (no extra added)
| Wall area | 8 × 8 × 16 in (standard) | 8 × 4 × 16 in half-high | 8 × 8 × 8 in half block |
|---|---|---|---|
| 20 sq ft | 23 | 45 | 45 |
| 50 sq ft | 57 | 113 | 113 |
| 100 sq ft | 113 | 225 | 225 |
| 200 sq ft | 225 | 450 | 450 |
How to use this calculator
- Measure the wall length and height (or the diameter of a round area). Use any unit — feet, inches, yards or meters.
- Split odd shapes into rectangles, circles and triangles, and add each one with “Add another area”.
- Pick a size and the joint width; the extra percentage covers cuts and breakage.
- Optionally enter a price to estimate the cost.
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Frequently asked questions
How many cinder blocks do I need for a 20 ft wall 4 ft high?
80 square feet × 1.125 = 90 blocks, or 95 with 5% extra.
What is the actual size of a cinder block?
An 8 × 8 × 16 block measures 7 5/8 × 7 5/8 × 15 5/8 inches, leaving room for a 3/8 inch mortar joint.