Cinder Block Calculator
A cinder block is a lightweight masonry unit in the standard 8 × 8 × 16-inch size, so it covers a wall at the same rate as a concrete block — about 1⅛ blocks per square foot. Enter the wall size for the block and mortar counts.
Blocks
189blocks
- Mortar (approx)
- 15 bags
- Wall area
- 160 sq ft
This estimates block and mortar quantities only — not structural design. Lightweight cinder block has load and below-grade limits; 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; the nominal 8×16-inch face (with its mortar joints) works out to about 1.125 blocks per square foot. Mortar runs about 7.5 pre-mixed bags per 100 blocks, or about 3 bags of masonry cement per 100 (plus sand), at 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: ≈15 pre-mixed bags, or ≈6 bags of masonry cement plus sand.
FAQs
- What's the difference between a cinder block and a concrete block?
- Both are concrete masonry units (CMU) in the same 8×8×16 size, so the count is identical. The difference is the aggregate: 'cinder' block uses lightweight cinders/ash and is lighter but weaker, while a true concrete block uses heavier stone aggregate and is stronger. Many building codes restrict lightweight cinder block from load-bearing or below-grade use — check yours.
- How many cinder blocks per square foot of wall?
- About 1.125 standard 8×8×16-inch blocks per square foot, once mortar joints are counted — the same as concrete block.
- How much mortar will I need?
- Roughly 7.5 pre-mixed (sand-included) bags per 100 blocks, or about 3 bags of masonry cement per 100 blocks if you mix your own sand, at standard ⅜-inch joints. Bag yield varies by brand.
Sources
- Cinder/concrete block (CMU) nominal 8×8×16 in; ≈1.125 blocks per sq ft. Mortar ≈7.5 pre-mixed 80-lb bags per 100 blocks, or ≈3 bags masonry cement per 100 (+ sand), at ⅜-in joints — verify by brand/joint.