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Concrete Calculator

Estimate how much concrete you need for a slab, in cubic yards and 80 lb bags.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-25 · v1.0.0

Market
Imperial · sales tax
9.84 ft9.84 ft0.33 ft
Schematic, drawn to the proportions you entered — not to scale on screen.
Who is doing the work?

The standard allowance most suppliers and estimating guides assume for ordinary work.

Estimated concrete needed

1.29 cubic yards

High confidence
Volume (no waste)
1.18 yd³
Volume with waste factor
1.29 yd³
Cubic feet
34.96 ft³
80 lb bags needed
59 bags

Official municipal inspection prerequisites — United States

Checked against ICC / ACI requirements for the currently selected market. Switching market re-runs these checks.

  • COMPLIANT — Concrete floor slabs on ground: minimum 3.5 in (89 mm) thick.

    Slab thickness 3.94 in meets the 3.5 in IRC floor-slab minimum. Expansive soils are handled separately under IRC R403.1.8, and any slab carrying vehicles or point loads should be designed rather than taken from the code minimum.

    IRC R506.1

These checks cover only the specific thresholds listed above. They are not a complete code review: fire separation, egress, structural capacity and accessibility provisions are outside their scope, and only the handful of local amendments offered in the selector are modelled — your municipality may have others. Final approval rests with your local building authority.

For the dimensions entered, expect a result of 1.29 cubic yards. Set for United States against IRC 2024. The market selector changes both the units and the code cited.

Estimated cost

$181 - $227

  • Ready-mix concrete, delivered$181 - $227

Estimated national-average pricing, adjusted by a rough regional multiplier — not a quote and not verified for your specific location or supplier. Last verified 2026-08-25.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Standard formula: cubic yards = length (ft) x width (ft) x thickness (ft) / 27
  • An 80 lb bag of pre-mixed concrete yields approximately 0.6 cubic feet once mixed

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Still deciding? Concrete Slab vs Pavers — the factors that actually differ, with no invented prices.

Frequently asked questions

Should I order exactly this amount from a ready-mix truck?
Order slightly more if you're unsure — ready-mix trucks usually charge a short-load fee for small orders anyway, and running short mid-pour is far worse than having a little extra.
How thick should my slab be?
4 inches (~0.1 m) is standard for patios, walkways, and shed floors. 6 inches (~0.15 m) is common for driveways carrying vehicle weight. Check local code for structural slabs.
Does this calculator account for rebar or wire mesh?
No — this estimates concrete volume only. Reinforcement is a separate material and structural decision, especially for driveways and load-bearing slabs.
Why 80 lb bags specifically?
80 lb bags are the most common size sold at hardware stores for DIY pours. If your bags are a different size, scale the bag count by the ratio of volumes.