🔵 Circular Concrete Calculator - Free 2026

Calculate circular concrete using the formula: Volume = π × radius² × depth. First, measure your circle's diameter and divide by 2 to get radius. Convert depth from inches to feet by dividing by 12. Multiply π (3.14159) × radius² × depth to get cubic feet, then divide by 27 for cubic yards.

Example: 10-foot diameter circle (5 ft radius) at 4 inches thick = π × 5² × (4/12) = 3.14159 × 25 × 0.333 = 26.18 cubic feet = 0.97 cubic yards. Add 10% waste factor = 1.07 cubic yards final order.

A 12-foot diameter round patio at standard 4-inch thickness requires approximately 1.4 cubic yards of concrete. This equals 63 bags of 80 lb concrete mix or one small ready-mix delivery. With 10% waste factor, order 1.54 cubic yards.

Cost ranges from $175-$210 for materials only (bagged mix) or $230-$280 for ready-mix delivery in 2026. Professional installation adds $500-$800 for labor, forming, and finishing, bringing total project cost to $730-$1,080 installed.

Diameter is the full width across a circle measured edge to edge through the center point - this is what most people measure first with a tape measure. Radius is exactly half the diameter, measured from the center point to any edge.

For concrete calculations, radius is used in the formula (π × r²) because it represents the distance from center. However, diameter is often easier to measure physically. Convert between them: Radius = Diameter ÷ 2, or Diameter = Radius × 2. A 16-foot diameter circle has an 8-foot radius.

A 10-foot diameter circular slab at 4 inches thick requires approximately 44 bags of 80 lb concrete mix (0.97 cubic yards base calculation). At 6 inches thick, you'll need 65 bags. With 10% waste factor included, order 48 bags for 4" thickness or 72 bags for 6" thickness.

Each 80 lb bag produces 0.60 cubic feet when mixed (0.022 cubic yards). For projects over 1 cubic yard, ready-mix delivery becomes more cost-effective than bags - compare $195 for 44 bags vs $150-$180 for bulk delivery including convenience and time savings.

Use whichever measurement is easier for you to obtain - our calculator handles both. Most people measure diameter first because it's straightforward: stretch a tape measure across the widest part of your circle. The calculator automatically converts diameter to radius for the formula.

If you're working from center stakes or existing markings, measuring radius directly from center to edge may be easier. For layout and forming, diameter determines your tape measure span. For calculations, radius goes into the formula (π × r²). Both methods produce identical results.

Use 3000 PSI concrete for residential circular patios, walkways, and general-purpose fire pits. This strength handles foot traffic, furniture weight, and moderate thermal stress. For fire pits with intense heat, consider high-temperature concrete mix with added insulation properties.

Upgrade to 3500-4000 PSI for round driveways, heavy equipment areas, or large fire features. For decorative thin overlays (3"), 3000 PSI is sufficient with proper reinforcement. Always use air-entrained concrete in freeze-thaw climates for durability regardless of PSI rating. See our concrete calculator for PSI recommendations by application.

Create perfect circular forms using the center stake method: Drive a stake at your circle's center point. Attach a string, chain, or rigid board equal to your radius length. Keep the string taut while walking around marking the perimeter every few feet with spray paint or flour.

For forming materials, use flexible hardboard (1/4" tempered), plastic landscape edging, or metal banding that bends smoothly without kinking. Stake the flexible material every 2-3 feet around your marked circle. Check radius measurements from center to form at multiple points to ensure perfect roundness before pouring concrete.

Yes, circular concrete typically costs 10-20% more than rectangular slabs of equivalent area due to specialized forming materials ($50-150 extra for flexible edging vs straight lumber), increased labor time for curved forming and finishing, and higher waste factors from cutting curves and edge trimming.

However, circles often use less total concrete than the enclosing square - a 12-foot circle uses 113 sq ft vs 144 sq ft for a 12×12 square, saving 21% on concrete volume. The material savings partially offset higher forming and labor costs. For projects under 200 sq ft, expect circular pours to cost $8-12 per square foot installed vs $6-9 for rectangular slabs.