DIY Cost Tools
Concrete Calculator
Convert slab dimensions into cubic feet, cubic yards, 80-pound bags, and an adjustable ready-mix material estimate.
How this calculator works
Volume = length × width × depth. Cubic yards = cubic feet ÷ 27. An 80-lb bag is estimated to yield 0.60 cubic feet.
How the estimate works: The calculator uses your measurements, unit conversions, waste allowance, and product coverage to create a planning quantity. Review the formula shown above, then read the matching guide below before ordering. See How Our Calculators Work for assumptions and limitations.
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These practical options match the work estimated by this calculator. Verify compatibility, specifications, and the current price before purchasing.
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Concrete quantity basics
Concrete is ordered by volume. Enter the finished length, width, and depth of a rectangular slab. The calculator adds your selected waste allowance and converts the result to cubic yards. Bag yield varies by brand and mix, so verify the number printed on the bag.
Important project checks
- Confirm excavation depth, compacted base, forms, reinforcement, and drainage.
- Ready-mix suppliers often have delivery minimums and short-load charges.
- Footings, thickened edges, piers, and slopes require separate calculations.
- Structural work should follow local code and approved plans.
Concrete slab example
A 10-by-12-foot slab at 4 inches thick contains 40 cubic feet of concrete. Dividing by 27 gives about 1.48 cubic yards. With a 10% allowance for grade variation, spillage, and uneven forms, the planning quantity becomes about 1.63 cubic yards. A ready-mix supplier may apply an order increment, delivery minimum, or short-load fee, so confirm how the final quantity must be rounded.
Separate every change in depth
Calculate thickened edges, footings, steps, piers, and sloped sections independently, then add the volumes. Use finished dimensions only after confirming excavation, compacted base, form placement, reinforcement, drainage, and local requirements. Bag yield varies by product and jobsite conditions; use the yield printed on the selected bag rather than assuming every 80-pound mix produces the same volume.