Concrete Calculator
Estimate concrete volume for a slab or a round column in cubic yards and cubic feet, including a flat 10% waste figure. It is not a mix design.
How to use
- Set Shape to Slab / Rectangle. Enter Length (ft), Width (ft), and Thickness (in). The sample is 10 feet by 10 feet by 4 inches.
- Press Calculate Volume. Slab volume in cubic feet is length times width times thickness divided by 12. The sample is 33.33 cubic feet, which is 1.23 cubic yards. The detail line also shows With 10% waste: 1.36 yd³.
- For a round pier, set Shape to Cylinder / Column. Width (ft) is hidden. Length (ft) stays labeled Length, but it is used as the diameter in feet. The third field changes from Thickness (in) to Height (ft), and that height is in feet, not inches.
- Press Calculate Volume again. Column volume is pi times radius squared times height, with radius equal to half the length field. The result is still cubic yards, with cubic feet and the same 10% waste line underneath.
When it helps
Use it before you call for a small patio, a sidewalk rectangle, or a single round footing when you already measured in feet and inches. The waste line is 10% more cubic yards than the geometric volume.
The form has no metric switch. Convert meters or centimeters on the unit converter first, then type feet and inches here. If you only need the area of a triangular patch beside the slab, the triangle calculator does base and height or three sides.
Limits
This is not a mix design and it does not count rebar. It never asks for cement, sand, gravel, water, slump, or PSI, and it does not convert yards into 60-pound or 80-pound bags.
One shape is calculated at a time. Cylinder mode does not rename Length (ft) to diameter, so typing the width into that field by habit will be wrong once width is hidden. Waste is always 10% of the cubic yards, not a factor you can edit, and the inch-to-foot divide applies only to the slab thickness.
Questions
Why did the third label change?
Choosing Cylinder / Column sets that label to Height (ft) and hides Width (ft). Slab / Rectangle sets it back to Thickness (in) and shows width again.
Is the 10% waste a design rule?
No. It is a flat pad on the cubic-yard result, shown beside the exact cubic feet. It does not account for spillage, an uneven subgrade, or extra cover over rebar, because rebar is not in the form.
Can I enter a 4-inch column height?
In cylinder mode the third field is Height (ft). Four inches of height must be typed as a fraction of a foot. Leaving 4 in that box means 4 feet.