Concrete block calculator
How many concrete blocks do I need?
Estimate the number of standard 8-inch concrete blocks for walls, foundations, and retaining walls.
Block calculator
Block calculator result
Block sizes and types
- Standard 8-inch block: 16 x 8 x 8 inches, most common for foundations
- 6-inch block: 16 x 8 x 6 inches, used for non-load-bearing walls
- 10-inch block: 16 x 8 x 10 inches, for retaining walls and thicker walls
- 12-inch block: 16 x 8 x 12 inches, for heavy-duty foundations
The calculator assumes standard 8-inch blocks. For other sizes, adjust the wall area and calculate manually.
Worked example
For example, for a 20×4 ft retaining wall, standard 8×16 in blocks:
- Wall area = 20 × 4 = 80 sq ft
- Block face area including ⅜-in joint = (16.375 × 8.375) ÷ 144 = 0.952 sq ft
- Blocks needed = 80 ÷ 0.952 = 84 blocks
- Add 5% for cuts: 84 × 1.05 = 88 blocks
- Also estimate mortar and rebar for larger walls
Common mistakes
| Mistake | Why it matters |
|---|---|
| Not using drainage gravel behind walls | Water pressure behind block walls causes bulging and failure |
| Skipping the base course leveling | A level, compacted gravel base for the first course is critical for wall alignment |
| Forgetting to stagger vertical joints | Stack blocks like bricks — offset each row by half a block for strength |