How Much Concrete for a 15 Foot Round Slab?
A round pad 15 feet in diameter covers about 176.7 square feet. How much concrete for a 15 foot round slab at 4 inches: 2.18 cubic yards, or about 99 bags of 80 lb mix.
Concrete calculator →The circle math
- Radius: 15 ÷ 2 = 7.5 ft.
- Area: 3.1416 × 7.5 × 7.5 = 176.7 sq ft.
- Volume at 4 in: 176.7 × 0.333 = 58.9 cu ft.
- Yards: ÷ 27 = 2.18 yd³.
A round slab takes about 21 percent less concrete than a square of the same width (15x15 would need 2.78 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 | 58.9 | 2.18 | 2.40 | 99 | 131 |
| 5 in | 73.6 | 2.73 | 3.00 | 123 | 164 |
| 6 in | 88.4 | 3.27 | 3.60 | 148 | 197 |
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 15 ft round slab?
About 2.18 cubic yards at 4 inches.
How many square feet is a 15 ft circle?
About 176.7 square feet.
How many 80 lb bags for a 15 ft round slab?
About 99 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 thick should the base under the slab be?
About 4 inches of compacted gravel is common for residential slabs, more on soft or poorly drained soil.
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 12 Foot Round Slab?
- How Much Concrete for a 14 Foot Round Slab?
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