Concrete Block Wall Calculator

Why This One Is Different

Framing a garden wall or a block foundation stem wall and need to know how many CMUs to order? This calculator divides your wall area by the block's coverage constant to get a net block count, adds a labeled 5% breakage-and-cuts allowance, and estimates mortar at roughly one 80 lb bag per 33 blocks, a trade convention, not a code figure. A concrete block wall is counted, not poured: the unit of measure is the block, and a standard 8×16 CMU face, mortar joint included, covers 0.889 square feet, a number that comes straight from the block's nominal modular dimensions rather than any manufacturer's marketing sheet. Load-bearing or retaining walls need engineering beyond a simple block count, so treat this as a materials estimate, not a structural design.

Where the Numbers Come From

• A standard 8×16 nominal CMU face covers 0.889 sq ft including the mortar joint, a definitional number from modular block sizing, not a manufacturer estimate. Source: CMHA (ex-NCMA) TEK notes on modular CMU dimensions and properties, via construction-estimating authoritative-source map
• A 5% breakage-and-cuts allowance is added on top of the net block count, a labeled trade convention accounting for corner cuts, openings, and normal handling loss. Source: trade convention, labeled as such (not codified in a standard)
• Mortar consumption runs approximately one 80 lb bag per 33 blocks, a trade convention that shifts with joint size and workmanship, not a fixed code figure. Source: trade convention, labeled as such (not codified in a standard)