Interactive Concrete slab calculator
Estimated result
Enter measurements and select Calculate.
How to use this calculator
- Measure each rectangular slab section separately.
- Enter the designed slab thickness in its actual unit.
- Add the section results for irregular layouts.
- Discuss order rounding, site access, and placement loss with the concrete supplier.
Formula and method
Slab volume = length × width × thickness. Convert to cubic yards by dividing cubic feet by 27, then apply the selected allowance.
Worked example
A 20 ft by 12 ft slab at 4 in thick contains 80 ft³, or about 2.96 yd³ before allowance.
Assumptions and result interpretation
- This is a volume-planning tool, not structural design approval.
- Footings, thickened edges, beams, and grade changes must be calculated separately.
- No bag yield or manufacturer-specific coverage is assumed.
Common mistakes
- Entering 4 inches as 4 feet
- Forgetting thickened edges
- Using nominal form dimensions without checking the site
- Treating the estimate as structural or code approval
Methodology sources
Conversions use deterministic factors. Variable material properties are either visibly sourced and editable or left for the user to enter from the supplier.
Results are planning estimates. Confirm actual requirements with the appropriate supplier, contractor, engineer, building official, or other qualified professional.