/// Short answer
concrete for a slab — the planning answer
To estimate concrete for a slab, multiply the measured slab length by width and finished depth, convert the volume to cubic yards, then add a clearly labeled waste allowance. A 10 ft × 10 ft slab at 4 in deep is 1.2346 yd³ before an allowance and 1.3580 yd³ with 10% waste. For bags, divide the adjusted volume by the exact package yield and round up; a supplier or qualified reviewer should confirm the final order.
How do you estimate concrete for a slab?
To estimate concrete for a slab, multiply the measured slab length by width and finished depth, convert the volume to cubic yards, then add a clearly labeled waste allowance. A 10 ft × 10 ft slab at 4 in deep is 1.2346 yd³ before an allowance and 1.3580 yd³ with 10% waste. For bags, divide the adjusted volume by the exact package yield and round up; a supplier or qualified reviewer should confirm the final order.
Rectangular slab volume = length × width × depth. Convert inches to feet before multiplying; divide cubic feet by 27 for cubic yards. Treat waste as an explicit planning input, not a hidden constant.
/// Continue with the numbers
Run the concrete calculator
Use this concrete calculator to enter each rectangular or circular pour separately, calculate net cubic feet and cubic yards, then apply a visible project-specific waste allowance. Optional 40, 50, 60, or 80 lb bag counts use only the selected QUIKRETE Concrete Mix No. 1101 yield and round up at the final package step.
/// Keep the topic connected
Related calculators
Use the neighboring tools to keep each material, layer, and order assumption visible instead of hiding it inside one estimate.
What should you measure first?
Measure the finished footprint rather than relying on a room, drawing, or property description. Depth is the most important input: a small change across a large slab changes the order substantially.
- Record length and width at more than one point if the edges are irregular.
- Measure the intended finished depth and note any thickened edge or separate pour.
- Confirm whether the supplier quotes ready-mix by cubic yard or you are using bagged product.
What should you verify before ordering?
The calculator produces a quantity estimate, not a slab design. Before ordering, confirm subgrade preparation, reinforcement, joints, access, placement method, local requirements, and the supplier's actual yield or truck minimum.
- Compare the calculated volume with a second manual calculation.
- Use the selected product data sheet for bag yield.
- Ask the supplier about minimum delivery quantity and overage policy.
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Related ProjectQty pages
/// Field-ready worksheet
Download the measurement checklist
Use the worksheet to record dimensions, product-label values, and verification notes locally. ProjectQty does not receive or store your project inputs.
/// Evidence trail
Sources and assumptions
This article inherits the calculator's declared source scope. Product yields, coverage, density, and label rates should be replaced with the exact product selected for the job.
Exact international-foot to meter conversion; U.S. survey-foot conversion is explicitly outside this claim.
NOAA National Geodetic Survey · Prequalified fallbackThe DSDATA Format, Appendix D: U.S. Survey Foot vs International FootIndependent confirmation that one international foot equals exactly 0.3048 meters; U.S. survey-foot conversion remains distinct.
The QUIKRETE Companies, LLC · Primary evidenceQUIKRETE Concrete Mix No. 1101-40 product yieldApproximate 0.3 ft³ yield for the 40 lb QUIKRETE Concrete Mix No. 1101-40 package only; not a generic bag-yield assumption.
The QUIKRETE Companies, LLC · Primary evidenceQUIKRETE Concrete Mix No. 1101-50 product yieldApproximate 0.375 ft³ yield for the 50 lb QUIKRETE Concrete Mix No. 1101-50 package only; not a generic bag-yield assumption.
The QUIKRETE Companies, LLC · Primary evidenceQUIKRETE Concrete Mix No. 1101-60 product yieldApproximate 0.45 ft³ yield for the 60 lb QUIKRETE Concrete Mix No. 1101-60 package only; not a generic bag-yield assumption.
The QUIKRETE Companies, LLC · Primary evidenceQUIKRETE Concrete Mix No. 1101-80 product yieldApproximate 0.6 ft³ yield for the 80 lb QUIKRETE Concrete Mix No. 1101-80 package only; not a generic bag-yield assumption.
/// Common questions
How Much Concrete Do You Need for a Slab? FAQ
Should slab waste be added before or after converting to cubic yards?
Either order is mathematically equivalent when the same percentage is used. ProjectQty applies the waste allowance to the base volume and shows the adjusted order quantity separately.
Can a concrete calculator choose the slab thickness?
No. Thickness depends on the project, loads, soil, reinforcement, climate, and local requirements. Enter the thickness from an approved project specification or qualified review.
How do I convert slab concrete to bags?
Use the exact bag size and published yield for the selected product. Divide the adjusted volume by that yield, then round up to whole bags.