Calculator guide
Estimate concrete volume for a rectangular slab, footing, or similar form.
Formula or method
Volume = length × width × depth. Convert cubic feet to cubic yards by dividing by 27; add a practical waste allowance separately.
How to use this calculator
- Enter length and width in a consistent unit.
- Enter the average depth.
- Review cubic feet and yards, then discuss ordering and waste with the supplier.
Worked example
A 20 ft × 10 ft slab at 4 in (1/3 ft) needs 66.67 ft³, or 66.67/27≈2.47 yd³; 10% allowance makes about 2.72 yd³.
Understanding the result
Order quantities are normally rounded up and depend on site shape, grade, and supplier minimums.
Limitations and assumptions
- Assumes a rectangular uniform depth and does not model thickened edges or irregular ground.
- Waste allowance is a planning choice, not a guarantee.
Frequently asked questions
Why use average depth?
A sloped or uneven base needs several sections or a site measurement.
Should I add waste?
Many projects allow roughly 5–10%, but ask the ready-mix supplier.
Does this include reinforcement?
No; rebar, forms, pumping, and finishing are separate.
Sources
Educational information only; verify important decisions with a qualified professional.