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Slab takeoff calculator
The whole slab package from dimensions: concrete (with waste), aggregate base (with compaction), and rebar grid footage — geometry-consistent, one pass.
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How it’s computed
Concrete cy = area × (thickness ÷ 12) ÷ 27 × (1 + waste). Base cy = area × (base depth ÷ 12) ÷ 27 × 1.12 compaction allowance. Rebar: bars each way at the grid spacing — (ceil(width ÷ grid) + 1) bars running the length plus (ceil(length ÷ grid) + 1) running the width. Defaults: 4" base, 18" grid, 10% waste. Example: a 12×51 slab at 6" → ~12.5 cy concrete, ~8.5 cy base, ~900 lf rebar.
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
Why 12% on the base?
Compacted aggregate places denser than delivered — the calculator carries a 1.12 factor on base volume so the order covers the compacted depth.
Does the rebar number include laps and chairs?
No — it's the grid run length. Splice laps, chairs/supports, and dowels into footings are added per your structural details.
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