Calculate the exact cubic yards, concrete bag count, weight, reinforcement, and 2026 material cost for any round concrete slab — patios, pads, footings, fire pit bases, well pads, and more — across all US regions.
A circular concrete slab calculator determines the volume of concrete required to pour a round slab of a specified diameter and thickness. Because the area formula involves π (3.14159), the math is less intuitive than for rectangular slabs — a 10-foot diameter slab has an area of 78.54 ft², not 100 ft² as many people assume. This calculator handles the geometry automatically, then converts cubic feet to cubic yards (dividing by 27) for ready-mix ordering, and to bag counts using the published yield for each QUIKRETE and Sakrete bag size. All results include a selectable waste factor and 2026 US pricing benchmarks.
For circular slabs under 0.5 cubic yards (e.g., a 4-ft diameter pad at 4 inches thick ≈ 0.16 CY), bagged concrete from a home improvement store is the practical choice — ready-mix trucks have a minimum delivery charge of $150–$250 regardless of volume. For slabs over 1 cubic yard, ready-mix is almost always cheaper: $130–$200/CY delivered versus $420–$540/CY effective cost using 80 lb bags at $7–$9 each. The breakeven point in 2026 is approximately 0.75–1.0 cubic yard.
The calculator uses the geometric volume formula for a cylinder (a circular slab is simply a very flat cylinder), applies your chosen waste factor, converts to cubic yards, and calculates bag count by dividing the adjusted volume in cubic feet by the published yield per bag.
Quick-reference table for the most common circular slab diameters at standard thicknesses. All bag counts use 80 lb bags (0.45 ft³ yield) with a 10% waste factor added:
| Diameter | Thickness | Net Area (ft²) | Net Volume (CY) | +10% CY | 80 lb Bags | Bagged Cost Est. | Ready-Mix Est. |
|---|---|---|---|---|---|---|---|
| 2 ft | 4 in | 3.1 | 0.04 | 0.04 | 3 | $21–$27 | Min. charge applies |
| 4 ft | 4 in | 12.6 | 0.16 | 0.17 | 11 | $77–$99 | Min. charge applies |
| 6 ft | 4 in | 28.3 | 0.35 | 0.39 | 24 | $168–$216 | Min. charge applies |
| 8 ft | 4 in | 50.3 | 0.62 | 0.69 | 42 | $294–$378 | $90–$138 |
| 10 ft | 4 in | 78.5 | 0.97 | 1.07 | 65 | $455–$585 | $139–$214 |
| 12 ft | 4 in | 113.1 | 1.40 | 1.54 | 93 | $651–$837 | $200–$308 |
| 12 ft | 6 in | 113.1 | 2.09 | 2.30 | 139 | $973–$1,251 | $299–$460 |
| 15 ft | 4 in | 176.7 | 2.19 | 2.41 | 145 | $1,015–$1,305 | $313–$482 |
| 20 ft | 4 in | 314.2 | 3.88 | 4.27 | 257 | $1,799–$2,313 | $555–$854 |
| 20 ft | 6 in | 314.2 | 5.82 | 6.40 | 385 | $2,695–$3,465 | $832–$1,280 |
Selecting the right slab thickness is critical. Under-sizing is the most common DIY mistake and leads to cracking, heaving, and premature failure:
| Application | Min Thickness | Recommended | Concrete PSI | Reinforcement | Code Guidance |
|---|---|---|---|---|---|
| Decorative Stepping Stone | 2 in | 2–3 in | 3,000 | None / Fiber | Non-structural |
| Landscape / Garden Pad | 3 in | 3–4 in | 3,000 | Fiber Mesh | Light use OK |
| Round Patio — Foot Traffic | 4 in | 4 in | 3,000 | 6×6 WWM or Fiber | ACI Minimum |
| AC / Equipment Pad | 4 in | 4–6 in | 3,000 | Fiber Mesh | Standard |
| Fire Pit Base | 4 in | 4–6 in | 3,000–3,500 | Rebar #3 or Fiber | Check heat rating |
| Well Pad / Pump Pad | 4 in | 6 in | 3,500 | Rebar #4 | Per local code |
| Driveway Apron (Cars) | 6 in | 6 in | 3,500 | Rebar #4 or WWM | ACI 330R |
| Column / Pier Footing | 8 in | 10–12 in | 4,000 | Rebar #4–#5 | Engineer required |
| Heavy Equipment Pad | 8 in | 10–12 in | 4,000–5,000 | Rebar #5 grid | Engineer required |
Bagged concrete prices have risen 12–18% since 2023. In 2026, 80 lb QUIKRETE 5000 averages $7.48–$8.97 at Home Depot and Lowe's nationally, with West Coast prices 10–15% higher than Midwest. The 90 lb Sakrete bag ($9–$12) offers the best yield per dollar for larger DIY projects. For slabs over 1 cubic yard, always get a ready-mix quote — even with delivery it is typically 30–50% cheaper than bagged concrete at retail.
Round slabs present a unique reinforcement challenge — standard rectangular rebar grids must be custom bent to fit circular forms. For patios and pads under 12 ft diameter, polypropylene fiber mesh (1.5 lb per CY added to the mix) is the easiest and most effective option. For larger slabs, 6×6 W1.4 welded wire mesh is cut in a circular shape. Column footings always require engineered rebar cages per ACI 318-19, typically #4 or #5 bars with a minimum 3-inch concrete cover.
ACI 308R recommends maintaining concrete at 50–95°F for at least 7 days for 3,000 PSI. Practical methods: wet burlap + plastic sheeting (most effective), curing compound spray (ideal for round shapes), or a wet soil berm around the perimeter. In hot dry climates (AZ, TX, NV) shade the slab immediately after finishing and mist every 30–60 minutes for the first 24 hours to prevent rapid surface drying and plastic shrinkage cracking.
Concrete volumes from dimension calculations are theoretical minimums. Real-world factors always increase consumption: uneven subgrade (even a 1-inch low spot adds significant volume to a large slab), material lost during transit and placement, and form measurement variations. The US industry standard is to order 5–10% more than calculated — this calculator applies that factor automatically. Running short of concrete mid-pour creates cold joints and structurally compromised sections that must be demolished and repoured. A small excess is always far cheaper than a second truck charge or tearing out a bad pour.
Industry standards and references used for 2026 USA circular slab volume, bag yield, and cost data
QUIKRETE® is the USA's largest bagged concrete manufacturer. Their published yield data (0.30 ft³ / 50 lb, 0.375 ft³ / 60 lb, 0.45 ft³ / 80 lb) forms the basis for all bag count estimates in this calculator.
Visit QUIKRETEACI 318-19 is the governing US standard for structural concrete design — providing minimum slab thickness, reinforcement requirements, concrete strength specifications, and cover requirements referenced in this calculator.
Visit ACIACI 308R is the American Concrete Institute's guide for curing concrete — covering duration, methods, and temperature requirements for all slab types including circular slabs in all US climate zones.
Visit ACI