Concrete Block Wall Calculator
Calculate the number of CMU blocks and bags of mortar for any wall - garden, retaining, foundation or shed.
The concrete block wall calculator handles CMU (concrete masonry unit) walls - garden walls, retaining walls, shed foundations, basement walls and freestanding fences. Enter the wall length, height and block size, and the calculator returns block count, mortar bags, sand volume and a typical rebar reinforcement estimate. The standard 8x8x16 CMU covers about 0.89 sq ft of wall face including the mortar joint, so 100 sq ft of wall = 112.5 blocks. Mortar usage averages 3 bags of 70lb premix per 100 blocks, but increases for half-blocks and larger blocks with more joint surface.
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Frequently asked questions
112-113 standard 8x8x16 CMU blocks per 100 sq ft of wall area, including a 5% waste factor for cuts and breakage. The block face is 8x16 inches (128 sq in), and including the 3/8 inch mortar joint, each block covers about 0.89 sq ft of wall.
Plan on 3 bags of 70lb mortar mix per 100 standard 8x8x16 blocks. For half-width blocks (4x8x16), expect more mortar per block because of the higher joint-to-area ratio - about 4 bags per 100. Type N mortar is standard for above-grade walls; Type S for below-grade or load-bearing.
Yes for any wall over 4 ft tall, all retaining walls and any load-bearing wall. Standard reinforcement is #4 rebar (1/2 inch) vertically every 32 inches and a horizontal bond beam every 4 ft of height. The cells get filled with grout where rebar runs. Check local building codes - requirements vary by region and wall use.
Mortar joins blocks together at the joints (typically 3/8 inch thick). Grout is a pourable cement mix that fills the hollow cells of CMU blocks to add structural strength, especially around rebar. Mortar is sticky and trowel-applied; grout is fluid and poured. Both use cement but with different sand/aggregate proportions.
Yes for the materials estimate, but retaining walls have additional requirements not in this calculator: drainage gravel behind the wall, weep holes every 4-8 ft, geogrid reinforcement for walls over 4 ft, and engineering plans for walls over 4 ft (most jurisdictions). Always check local code before building a retaining wall.