The Block CalculatorHow does this cinder block wall calculator work?
Enter the wall’s length and height and the face size of your cinder blocks. The calculator divides the areas and rounds up. For a US 8″ × 8″ × 16″ block, enter 16 × 8 inches so the mortar joint is included.
Cinder block wall quick reference
- Blocks per square foot: 1.125 (8″ × 16″ face).
- Blocks per 100 sq ft: 112.5, so order about 118–124 with waste.
- Courses in an 8 ft wall: 12 courses of 8″ blocks.
Need to fill the cores? Use the concrete block fill calculator to work out grout volume and bag count.
Formula used
Total Blocks = (Wall Length × Wall Height) ÷ (Block Length × Block Height)The result is always rounded up to the next whole block, because you can’t buy part of one. Wall thickness is shown in the diagram but does not change the count for a single-wythe wall.
Example
Scenario: A wall 10 m long and 2 m high, built with cinder blocks measuring 40 cm × 20 cm (0.4 m × 0.2 m).
Wall area: 10 m × 2 m = 20 m²
Cinder block face area: 0.4 m × 0.2 m = 0.08 m²
Final result: 20 ÷ 0.08 = 250 cinder blocks. Add 5–10% for cuts and breakage when you order.
Frequently asked questions
How many cinder blocks for a 4 ft high, 20 ft long wall?
80 sq ft × 1.125 = 90 blocks, plus waste, so about 95–99 blocks.
Do cinder block walls need rebar?
Structural and retaining walls usually need vertical rebar in grouted cores. Low garden walls may not, so check local code and your engineer’s advice.
Last updated: . Results are estimates — see our disclaimer.