Concrete Block Calculator
A standard concrete block (CMU) is 8 × 8 × 16 inches, and it takes about 1⅛ blocks to cover a square foot of wall. Enter the wall size for the block count and mortar.
Blocks (8×8×16)
189blocks
- Mortar (approx)
- 15 bags
- Wall area
- 160 sq ft
This estimates block and mortar quantities only — not structural design. Footings, reinforcement, grouting, and bond must follow engineered plans and local code.
How it’s calculated
Blocks = wall area × 1.125 × (1 + waste), rounded up. Wall area is length × height; a nominal 8×16-inch block face (with its mortar joints) works out to about 1.125 blocks per square foot. Mortar depends on the product: pre-mixed mortar (sand already in, 80-lb bags) runs about 7.5 bags per 100 blocks, while masonry cement mixed with sand on site is about 3 bags per 100 (plus the sand), at standard ⅜-inch joints.
Worked example
A 20 ft × 8 ft wall = 160 sq ft × 1.125 = 180 blocks, × 1.05 for 5% waste = 189 blocks. Mortar: with pre-mixed bags, 189 ÷ 100 × 7.5 ≈ 15 bags; with masonry cement + sand, 189 ÷ 100 × 3 ≈ 6 bags (plus sand).
FAQs
- How many concrete blocks are in a square foot of wall?
- About 1.125 standard 8×8×16-inch blocks per square foot, once the mortar joints are accounted for. That's the figure this calculator uses.
- How much mortar do concrete blocks need?
- It depends on the product. Pre-mixed mortar — the 80-lb bags from a big-box store, with sand already in — runs about 7.5 bags per 100 blocks. Masonry cement that you mix with your own sand is about 3 bags per 100 blocks, plus the sand. Bag yield and joint size move both, so treat them as planning figures.
- Does this work for cinder block?
- Yes — lightweight 'cinder' block shares the 8×8×16 nominal size and the same ~1.125-per-square-foot count. The difference is weight and aggregate, not dimensions.
Sources
- Standard CMU is 8×8×16 in nominal; ≈1.125 blocks per sq ft of wall. Mortar ≈7.5 pre-mixed 80-lb bags per 100 blocks, or ≈3 bags of masonry cement per 100 (plus sand), at ⅜-in joints; varies by brand and joint size — verify.