How this calculator works
Convert slab dimensions to cubic feet and cubic yards, then estimate bag counts from a selectable bag yield.
Volume = length × width × thickness in feet. Apply waste, divide by 27 for cubic yards, or divide cubic feet by bag yield for bag count.
Example
A 12 × 10 ft slab at 4 inches thick is about 1.48 cubic yards before waste.
How to get a better estimate
- Subgrade depth and form dimensions should be measured, not assumed.
- Bag yield varies by bag size and mix.
- Large pours are usually more practical as ready-mix.
What the result means
The result is a planning estimate. Dimensions, coverage, density, packaging and installation conditions vary by product and project. For purchasing, compare the result with the exact product label or supplier specification. For structural, electrical, code-regulated or safety-critical work, use an appropriately qualified professional.
Common questions about the Concrete Calculator
What does this calculator estimate?
Convert slab dimensions to cubic feet and cubic yards, then estimate bag counts from a selectable bag yield.
What formula does it use?
Volume = length × width × thickness in feet. Apply waste, divide by 27 for cubic yards, or divide cubic feet by bag yield for bag count.
How should I use the result?
Use it as a planning estimate, then verify the dimensions and replace editable defaults with the specifications for the product or service you actually intend to buy.
Reference tables
Want a fast benchmark without changing inputs? These static tables use the same published calculation method.