BuildCalc

Concrete Slab Calculator

Estimate everything a concrete slab needs — volume, bags, ready-mix cost and rebar. Enter the slab length, width and thickness and the calculator returns the cubic yards, the number of 80 lb bags, an estimated ready-mix price and the rebar for a 16 in grid, all with a waste allowance.

Concrete for the slab
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    How it works

    Volume (cu ft) = length × width × (thickness ÷ 12); cubic yards = cu ft ÷ 27. Ready-mix cost = cubic yards (plus waste) × your price per cubic yard. Rebar assumes a 16 in on-center grid in both directions. 80 lb bags = cu ft ÷ 0.60, rounded up.

    Frequently asked questions

    How thick should a concrete slab be?

    Patios, sheds and walkways are usually 4 inches thick; garage floors and slabs that carry vehicles are typically 5–6 inches. Follow local code for structural slabs.

    How many bags of concrete for a slab?

    For small slabs, divide the volume in cubic feet by the bag yield (80 lb ≈ 0.60 cu ft). A 10 × 10 ft slab at 4 in is about 12.3 cu ft, so roughly 23 bags of 80 lb — usually the point where ready-mix or a trailer of concrete is cheaper.

    Does this include rebar and cost?

    Yes — it estimates rebar for a 16 in on-center grid and a ready-mix cost from the price per cubic yard you enter. Both are planning estimates; confirm reinforcement with your local code.

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    All concrete calculators

    Estimates are for planning only. Material yields, densities and code requirements vary — confirm quantities with your supplier and local building code before ordering.