Circular Concrete Slab Calculator
Estimate concrete volume, full bag quantity, round surface area, circumference, placed weight and cost for one or more circular slabs.
Default project preview
2.73 yd³
Concrete bags
123
Base volume
2.48 yd³
Round surface area
201.1 ft²
Edge circumference
50.3 ft
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Input and output guide
What each value means
The labels and units below are part of this calculator’s visible methodology. Replace every default with measurements or product data from the actual project.
Slab diameter
Enter this project assumption in ft. The current imperial default is 16 ft.
Slab thickness
Enter this project assumption in in. The current imperial default is 4 in.
Equal slabs
Enter this project assumption in a unitless value. The current imperial default is 1. Minimum: 1.
Waste allowance
Enter this project assumption in %. The current imperial default is 10 %. Minimum: 0. Maximum: 50.
Concrete yield per bag
Enter this project assumption in ft³. The current imperial default is 0.6 ft³.
Ready-mix price
Enter this project assumption in per yd³. The current imperial default is 165 per yd³. Minimum: 0.
Price per bag
Enter this project assumption in a unitless value. The current imperial default is 7. Minimum: 0.
How to read the outputs
Concrete bags
rounded full bags. Default preview: 123.
Base volume
before waste. Default preview: 2.48 yd³.
Round surface area
all slabs. Default preview: 201.1 ft².
Edge circumference
all slab edges. Default preview: 50.3 ft.
Placed weight
planning density. Default preview: 11,046 lb.
Cost comparison
ready-mix / bags. Default preview: $450.53 / $861.00.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Area = π × radius² × quantity. Concrete volume = area × thickness. Waste is applied before converting to ready-mix volume or rounding bags up.
Reviewed project guidance
How to use this estimate in a real project
Last reviewed: July 30, 2026
Estimate concrete volume for circular pads from diameter and thickness, including order allowance and whole-batch rounding.
Calculation steps
- 1Enter the actual project dimensions or operating values.
- 2Apply the calculator formula using consistent units.
- 3Review the unrounded result and the editable allowance.
- 4Round only to the product, stock length or equipment increment actually purchased.
Worked numerical example
A 12 ft diameter slab 5 in thick contains about 1.75 yd³ and may be ordered as roughly 1.9 yd³ with 8% allowance.
Purchasing and rounding
Order ready-mix by the supplier's accepted volume increment after converting the circular slab volume to cubic yards or cubic metres. Keep the placement allowance separate from the geometric volume, and confirm whether the supplier has a minimum-load or short-load charge before rounding the order.
Interpret the result
The geometric result is the concrete contained in a perfect circular slab at the entered thickness. The order quantity should be slightly higher for grade variation, forms and placement loss, but structural thickness, reinforcement and subbase requirements must come from the project design.
Page-specific assumptions
- Inputs describe one consistent project condition.
- Entered yields and efficiencies match the selected product or equipment.
- Site-specific code and engineering requirements are checked separately.
Common mistakes
- Mixing imperial and metric inputs.
- Using nominal dimensions where actual coverage controls.
- Rounding intermediate values too early.
- Treating a quantity estimate as design approval.
Primary and technical references
BuildMeter provides planning estimates, not engineering, architectural, electrical, mechanical, plumbing, permit or code approval. Review the methodology and verify final decisions with product documentation and qualified professionals.
FAQ
Circular Concrete Slab Calculator questions
Should diameter be measured to the form interior?+
Yes. Use the intended finished concrete diameter inside the form.
Does this include a thickened edge?+
No. It assumes one uniform slab thickness across the full circle.
Can this calculate a circular footing?+
It estimates volume, but structural footing dimensions and reinforcement require an approved design.