How many bags of concrete do I need for a 10x10 slab at 4 inches thick?

A 10 ft × 10 ft × 0.333 ft slab equals about 33.3 cubic feet, or roughly 1.23 cubic yards. With a 10% waste factor, that's approximately 37 cubic feet of mixed concrete — about 62 bags of 60 lb mix or 47 bags of 80 lb mix. Our calculator computes this instantly once you enter those dimensions.

What is the standard thickness for a concrete driveway or patio slab?

Residential driveways are typically poured at 4 inches thick for passenger vehicles, and 5–6 inches if you expect heavier loads like RVs or delivery trucks. Patios and walkways generally call for a minimum of 3.5–4 inches. Always check local building codes, as some jurisdictions specify minimums.

How do I convert cubic feet to cubic yards for a concrete order?

Simply divide your total cubic feet by 27, since one cubic yard equals 27 cubic feet. For example, 54 cubic feet ÷ 27 = 2 cubic yards. This calculator performs that conversion automatically.

Can I use this calculator for circular slabs or round footings?

This tool is optimized for rectangular slabs and footings. For a circular slab, calculate volume manually using π × radius² × thickness in feet, then divide by 27 for cubic yards — or enter the result directly into our unit converter. A dedicated circular slab calculator is on our roadmap.

How deep do concrete footings need to be?

Footings must extend below the local frost line to prevent heaving, which ranges from about 12 inches in the deep South to 48 inches or more in northern states and Canada. Additionally, local codes often specify a minimum footing depth and width based on the load being supported. Always verify with your local building department before excavating.

How much does a cubic yard of concrete weigh?

A cubic yard of standard ready-mix concrete weighs approximately 3,900 to 4,050 pounds (about 1,770–1,840 kg), depending on the aggregate used. This is an important consideration for estimating truck delivery logistics and for temporary formwork load calculations.

Should I add a waste factor when ordering concrete, and how much?

Yes — a 10% waste factor is the industry-standard recommendation for most pours to cover spillage, subgrade low spots, and mixing losses. For irregular or hand-excavated forms, increase this to 15%. The calculator includes this buffer by default, but you can adjust it to match your site conditions.

What's the difference between cement and concrete?

Cement is the binding powder (typically Portland cement) that is one ingredient in concrete. Concrete is the finished mixture of cement, water, sand, and coarse aggregate (gravel or crushed stone). When you buy 'bags of concrete mix,' the cement, sand, and aggregate are already pre-blended — you just add water.

Concrete Calculator

Concrete volume for slabs & footings in cubic yards/meters, plus bags needed.

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Length (ft)

Width (ft)

Thickness (inches)

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Concrete needed

1.23 yd³

0.94 m³ · 33.3 ft³

Cubic yards

1.23

80 lb bags

60 lb bags

AI Breakdown & Smart Takeaway

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How the Concrete Calculator works

The GKCalculators Concrete Calculator helps homeowners, contractors, and DIYers instantly determine the volume of concrete needed for slabs and footings in cubic yards or cubic meters, then converts that volume into the number of premixed bags required — eliminating guesswork and costly overorders.

For a rectangular slab, the calculator multiplies length × width × thickness (all converted to a consistent unit) to produce the raw volume. Because concrete in the US is ordered by the cubic yard, the result is divided by 27 (the number of cubic feet in a cubic yard). For metric users, dimensions entered in centimeters or meters yield a direct cubic-meter result. Even a small error in thickness — say, entering 4 inches versus the actual 4.5 inches — compounds across a large pour and can leave you a quarter-yard short, so the calculator prompts you to double-check every dimension before computing.

Footings follow the same volume formula but typically involve a rectangular cross-section that runs along a linear path rather than covering a flat area. The tool handles this by treating the footing as a long rectangular prism: footing width × footing depth × total linear length. For projects with multiple footing runs (e.g., a full perimeter foundation), users can sum each run separately or enter the total linear footage, and the calculator aggregates the volume. Getting footing depth right is especially critical because footings must often extend below the frost line — 12 to 48 inches depending on climate — which dramatically affects the cubic-yard total.

Once the total concrete volume is known, the calculator converts it into the number of premixed bags needed, a critical step for DIY projects where renting a mixer or ordering ready-mix is not practical. Standard 60 lb bags yield approximately 0.45 cubic feet of mixed concrete, while 80 lb bags yield about 0.60 cubic feet. The tool applies these yields automatically based on your selected bag size. It also adds a default 10% overage allowance — a best practice endorsed by most concrete industry guides — to account for spillage, subgrade irregularities, and slight volume loss during mixing. Users can adjust this waste factor if site conditions call for more or less buffer.

One common mistake is forgetting to convert all dimensions to the same unit before calculating. Entering length in feet but thickness in inches without conversion produces a wildly incorrect volume. This calculator handles unit conversion internally, but users should still verify that they're measuring the actual finished thickness of the pour, not the thickness of the formwork lumber. Another frequent error is neglecting to account for reinforcement displacement; rebar and wire mesh occupy a small volume, but for large pours it's worth noting that most estimators simply absorb this into the standard waste factor rather than calculating it separately.

Formula

Volume (ft³) = Length (ft) × Width (ft) × Thickness (ft); Cubic Yards = Volume (ft³) ÷ 27; Bags Needed = [Volume (ft³) × (1 + waste factor)] ÷ Yield per bag (ft³)

Pro tips

Always measure your slab thickness at the thinnest point of the subgrade, not the average — concrete must meet minimum thickness everywhere, and a low spot you didn't account for will consume extra material fast.
For large pours exceeding 1 cubic yard, price out ready-mix concrete delivered by truck against the cost of bagged cement; ready-mix is almost always cheaper and faster above that threshold, and this calculator's cubic-yard output makes it easy to call a supplier with an accurate order.
When estimating footing volume for a full foundation perimeter, measure the centerline length of each wall rather than the outer edge to avoid double-counting corner volumes — a subtle but real source of overestimation.
Increase your waste factor to 15% if you're pouring into irregularly shaped or hand-dug excavations, where the bottom and walls are unlikely to be perfectly uniform.
Order bags in the largest size you can safely handle (80 lb); fewer bags means less mixing time, fewer open bags left over, and a lower per-cubic-foot cost compared with 40 lb or 60 lb options.

Key terms

Cubic Yard: — The standard unit for ordering ready-mix concrete in the United States, equal to 27 cubic feet (3 ft × 3 ft × 3 ft).
Slab: — A flat, horizontal concrete pad — such as a driveway, patio, or floor — whose volume is calculated by multiplying its length, width, and uniform thickness.
Footing: — A below-grade concrete element that distributes structural loads from walls or columns into the soil, typically calculated as a linear rectangular prism defined by width, depth, and run length.
Yield: — The volume of mixed concrete produced by one bag of dry premix, typically 0.45 ft³ for a 60 lb bag and 0.60 ft³ for an 80 lb bag.
Waste Factor: — A percentage added to the calculated volume (commonly 10%) to account for spillage, uneven subgrades, and mixing losses, ensuring you don't run short on pour day.
Frost Line: — The maximum depth to which soil is expected to freeze in a given climate zone; footings must be placed below this depth to prevent frost-heave damage to the structure.