How Much Concrete for a 20 Foot Round Slab?
How much concrete for a 20 foot round slab: about 3.88 cubic yards at 4 inches thick. A circle 20 feet across has a radius of 10 feet and an area of about 314.2 square feet (π × 10²).
Concrete calculator →The circle math
- Radius: 20 ÷ 2 = 10 ft.
- Area: 3.1416 × 10 × 10 = 314.2 sq ft.
- Volume at 4 in: 314.2 × 0.333 = 104.7 cu ft.
- Yards: ÷ 27 = 3.88 yd³.
A round slab takes about 21 percent less concrete than a square of the same width (20x20 would need 4.94 yards at 4 inches).
Related: How Much Concrete for a 24 Foot Round Slab?
By thickness
| Thickness | Cubic feet | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 104.7 | 3.88 | 4.27 | 175 | 233 |
| 5 in | 130.9 | 4.85 | 5.33 | 219 | 291 |
| 6 in | 157.1 | 5.82 | 6.40 | 262 | 350 |
Forming a circle
Mark the circle with a stake and a string the length of the radius. Flexible form material such as hardboard strips or plastic forms bends to the curve; stake it closely, since curves push outward when the concrete goes in.
Related: How Much Concrete for a 24 Foot Round Slab?
Common uses and thickness
Round pads are popular for fire pit seating areas, grill stations, gazebos and tank bases. Four inches suits foot traffic and furniture; a gazebo, hot tub or tank needs a thicker slab and a well-compacted base, and a tank base may have engineering requirements.
Joints in a round slab
Cut control joints like pie slices from the center outward, with an optional ring joint for larger circles, so each panel stays a manageable size.
Questions people ask
How many yards of concrete for a 20 ft round slab?
About 3.88 cubic yards at 4 inches.
How many square feet is a 20 ft circle?
About 314.2 square feet.
How many 80 lb bags for a 20 ft round slab?
About 175 bags at 4 inches thick.
How do I find the area of a circle?
Multiply 3.1416 by the radius squared. The radius is half the diameter.
How many 80 lb bags make a cubic yard?
About 45. Each 80 lb bag yields roughly 0.6 cubic feet, and a cubic yard is 27 cubic feet.
Related guides
- How Much Area Does a Yard of Concrete Cover?
- How Many Bags of Concrete in a Yard? 40, 60, 80 lb
- Gravel Base Under a Concrete Slab: Depth and Tons
- How Many Yards in a Concrete Truck? Mixer Sizes
- Concrete Short Load Fee: What It Is and How to Cut It
- 60 lb vs 80 lb Concrete Bags: Yield, Count, and Cost
- Rebar vs Wire Mesh in a Slab: Which One to Use
- Gravel for a Fire Pit Area: Best Types and Depth
- How Much Concrete for a 16 Foot Round Slab?
- How Much Concrete for an 18 Foot Round Slab?
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