Concrete Slab Calculator

Calculate cubic feet, cubic yards, ready-mix quantity, and bag counts for a rectangular concrete slab from length, width, thickness, and waste.

Quick answer

Concrete slab quick answer

Answer: Concrete slab volume is the slab length multiplied by width and thickness, converted into cubic yards for ready-mix ordering.

Formula: Cubic yards = length (ft) × width (ft) × thickness (ft) ÷ 27. Apply the chosen waste allowance after calculating base volume.

Example: A 10 ft × 10 ft slab that is 4 inches thick is about 1.23 cubic yards before waste.

Reviewed September 1, 2026 · Methodology

Slab length (ft)Slab width (ft)Thickness (in)Extra allowance (%)Bag size / yield

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Enter your measurements and calculate.

Worked example

Example

A 10 × 10 ft slab at 4 inches thick is about 33.33 cu ft. With 10% extra, that is about 1.36 cu yd or roughly 62 sixty-pound bags.

References

Sources & assumptions

Last reviewed September 1, 2026. Defaults are starting points; product-specific inputs are editable wherever coverage varies.

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FAQ

Common questions

How many cubic feet are in a cubic yard?

27 cubic feet.

How much does an 80 lb bag yield?

A common published yield is about 0.60 cubic foot, but verify your exact mix.

Should I add extra concrete?

An allowance can help cover grade variation, spillage, and measurement error. Your project may require a different amount.

Public API & AI agent access

Yes — Concrete Slab Calculator is callable programmatically through /api/v1/concrete-slab, the public calculator API, MCP, A2A and WebMCP. Structured results include a human-facing citation URL.

Formula provenance

API identifier: concrete-slab · Formula version: tncalc.concrete-slab.1.0.0 · Engine release: 6.6.1. Build provenance · Public validation · Release history.

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