Question: how to figure how much concrete for a circle?
Answer: Area. A = π * D² ÷ 4. ... 
Perimeter. ... 
Volume. ... 
Example calculation for volume: Diameter of slab = 12 feet depth of slab = 4 inches 3.14159265358979 * 12 * 12 ÷ 4 ( 4 ÷ 12) 113.09 * 0.333 = 37.7 cubic feet of concrete needed for this circular slab To convert cubic feet to cubic yards multiply cubic feet * 0.037037037037037.