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Concrete Volume Calculator

Whatever the shape of the pour, a rectangular slab or a round pad or footing, get the volume in cubic yards for ordering ready-mix, plus the bag count if you'd rather mix it yourself.

Diagram of a concrete pour as a box, showing length, width and depth
Any pour is a box: length × width × depth gives the volume to order.

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Enter your measurements

How the volume is calculated

For a rectangular pour, volume is length × width × thickness, with thickness converted from inches to feet. For a round pour it's the cylinder formula: π × (diameter ÷ 2)² × depth. Multiply by the number of identical pours, then divide cubic feet by 27 to get cubic yards.

Ready-mix is sold in quarter-yard steps, so the order figure adds your waste allowance and rounds up to the nearest 0.25 cu yd, the same convention the Concrete Slab Calculator uses. The bag alternative uses the yields both Quikrete and Sakrete publish: an 80 lb bag makes 0.60 cu ft, a 60 lb bag 0.45 cu ft, a 40 lb bag 0.30 cu ft.

For a specific slab with costings, use the slab calculator; for bags only, the Concrete Bag Calculator goes deeper on bag choice. For post holes and round footings specifically, the Post Hole Calculator counts bags per hole.

Sources

The figures behind this calculator come from published manufacturer data and industry standards:

Worked examples

20 × 12 ft pour, 6 in thick

120 cu ft = 4.44 cu yd exact. 10% waste, quarter-yard rounding.

Order 5 cu yd

Round pad, 10 ft across, 12 in deep

78.5 cu ft = 2.91 cu yd exact. 10% waste, or 192 × 60 lb bags.

Order 3.25 cu yd

Two 12 × 8 ft slabs, 4 in thick

64 cu ft combined = 2.37 cu yd exact. 10% waste.

Order 2.75 cu yd

Frequently asked questions

How do I convert cubic feet of concrete to cubic yards?
Divide by 27. A cubic yard is 3 ft × 3 ft × 3 ft. A 10×10 ft slab 4 in thick is 33.3 cu ft, which is 1.23 cu yd.
How much concrete does a round footing need?
Use the cylinder formula: π × radius² × depth. A 12 in diameter hole 36 in deep is about 2.36 cu ft, roughly four 80 lb bags before waste allowance.
Why order more than the exact volume?
Subgrade is never perfectly level, forms bow slightly, and some concrete stays in the chute and tools. A 10% allowance is standard for flatwork; running short mid-pour is far costlier than a little extra.
When is ready-mix better than bags?
Once a pour passes about a cubic yard, bags become slow, heavy work. One yard is 45 × 80 lb bags. Ready-mix also gives a consistent mix and a single continuous pour, which matters for strength.

Related calculators

Concrete Bag Calculator

How many 40, 60 or 80 lb bags of concrete you need, and what they'll cost.

Concrete Slab Calculator

Cubic yards of ready-mix for a slab, plus the bag count if you mix it yourself.

Concrete Block (CMU) Calculator

Blocks and mortar bags for a block wall.

Rebar Calculator

Rebar pieces and grid layout for a slab.

Estimate disclaimer: results are planning estimates based on standard manufacturer yields and coverage figures. Site conditions, product choice and installation method change actual quantities. Verify before you buy, and follow local building code for structural work. This tool does not replace professional engineering advice.

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