How do I calculate concrete cubic yards for a slab?
Rectangular volume = length × width × thickness. Column volume = π × radius² × depth × count. Convert to cubic yards, add waste, then divide by bag yield if needed.
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Concrete calculator
Calculate concrete volume and bag quantities for slabs, footings, walls, and columns.
- Metric and imperial units
- Instant updates as inputs change
- Data is calculated in this browser only
Results are planning estimates. Confirm site dimensions, product specifications, and installation waste before purchasing.
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Calculation notes
Understand the Concrete calculator
Slabs, footings, and walls use length × width × thickness. Columns use count × π × radius² × depth. Volumes are summed, waste is added, and the result is divided by bag yield.
How much concrete is needed for a 12 by 10 ft slab 4 in thick?
A 12 × 10 ft slab at 4 in thick is 40 cu ft, or about 1.48 cu yd. With 10% waste, order about 1.63 cu yd.
How should ready-mix yards and concrete bags be rounded?
- For ready-mix, round according to the supplier’s minimum increment.
- For bagged concrete, select the exact bag size and labeled yield.
Why should a concrete order include a waste allowance?
- Thickness entered in inches or centimeters is converted before volume is calculated.
- For larger pours, confirm minimum orders and delivery terms with a local ready-mix supplier.
- Excavation tolerance, subgrade variation, forms, and spillage can increase volume.
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