Concrete Calculator: Circular Slab Volume
Estimate the concrete volume for a circular slab in seconds. Enter diameter or radius, the slab thickness, and a waste allowance. You will get area and volume in multiple units, plus approximate bag counts. Notes, formulas, and FAQs are included for clarity.
Results
Net area
0.000 m²
Net volume
0.000 m³
0.000 yd³
0.00 ft³
With waste
0.000 m³
0.000 yd³
0.00 ft³
Approximate bag counts
US bag sizes (QUIKRETE® yield)
Yields per bag from QUIKRETE data sheet. Actual yield varies by placement and compaction. Source
Metric bag sizes
Default yields are common published figures. Edit to match your local product.
How to use this concrete calculator
- Select metric or US units.
- Choose whether you are entering a diameter or a radius, then input the value.
- Enter the slab thickness and a waste allowance. Many jobs add 4 to 10 percent for waste.
- Optionally subtract a circular opening such as a sump or pipe sleeve.
- Read the area, volume, and bag counts. Round up when ordering.
Formulas and assumptions
- Area of circle:
A = πr². If you enter diameterD, radiusr = D/2. - Volume:
V = A × Twhere thicknessTis converted to meters internally soVis in m³. - Opening: Net area = slab area minus opening area
π(Ropen)². - Waste:
Vwaste = V × (1 + waste%). - Bag counts: bags =
Required volume ÷ bag yield. US yields use ft³ per bag. Metric yields are editable in m³ per bag. - Typical slab thickness: many residential slabs are about 4 in (≈100 mm). Always follow local code and your engineer.
References
- Waste allowance 4 to 10 percent: NRMCA Concrete In Practice CIP 8, CIP 31
- Minimum slab thickness on ground: 2021 IRC R506, 3.5 in ICC
- US bag yields: QUIKRETE® Concrete Mix 1101 data sheet
FAQs
How do I measure the diameter accurately?
Measure across the widest part of the circle from edge to edge through the center. If you have the circumference, divide by π to get the diameter.
Can I enter radius instead of diameter?
Yes. Choose Radius in the Size input selector and enter the radius directly.
Should I add reinforcement to a circular slab?
Follow your engineer and local code. Reinforcement depends on load, soil, and slab size.