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Cinder block (CMU) calculator
Block and mortar for a CMU wall from its dimensions — openings subtracted, waste included.
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How it’s computed
Wall sqft = length × height − openings (clamped at 0). Blocks = ceil(wall sqft ÷ block face × (1 + waste)) using NOMINAL face dimensions — the default 8×16 nominal (joint included) works out to 1.125 block/sqft, the takeoff standard. Mortar ≈ 3 bags per 100 block (Type N/S, 8" CMU). Default 5% waste.
Decimal-exact and deterministic: identical inputs always return identical results. This is the same math Ask Donnie’s estimating engine runs — not an approximation, and never a language model doing arithmetic.
Common questions
Nominal vs actual block size?
Nominal 8×16 includes the 3/8" mortar joint (actual block is 7-5/8 × 15-5/8). Takeoffs use nominal face size precisely so the joint is already counted.
What about grout, rebar, and filled cells?
Structural — per your engineer's schedule. This calculator counts block and bedding mortar only.
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