How Much Concrete for a 12 Foot Round Slab?
A round pad 12 feet in diameter covers about 113.1 square feet. How much concrete for a 12 foot round slab at 4 inches: 1.40 cubic yards, or about 63 bags of 80 lb mix.
Concrete calculator →The circle math
- Radius: 12 ÷ 2 = 6 ft.
- Area: 3.1416 × 6 × 6 = 113.1 sq ft.
- Volume at 4 in: 113.1 × 0.333 = 37.7 cu ft.
- Yards: ÷ 27 = 1.40 yd³.
A round slab takes about 21 percent less concrete than a square of the same width (12x12 would need 1.78 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 | 37.7 | 1.40 | 1.54 | 63 | 84 |
| 5 in | 47.1 | 1.75 | 1.92 | 79 | 105 |
| 6 in | 56.5 | 2.09 | 2.30 | 95 | 126 |
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
Fire pit patios, gazebo floors and tank pads are the usual round slabs. For people and furniture, 4 inches on compacted gravel is standard. Anything heavy needs more thickness and possibly reinforcement; check the manufacturer’s requirements for tanks or bins.
Joints in a round slab
Radial joints from the center keep cracks in check. On larger circles, a ring joint partway out keeps the outer panels from getting too long and narrow.
Questions people ask
How many yards of concrete for a 12 ft round slab?
About 1.40 cubic yards at 4 inches.
How many square feet is a 12 ft circle?
About 113.1 square feet.
How many 80 lb bags for a 12 ft round slab?
About 63 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 an 8 Foot Round Slab?
- How Much Concrete for a 10 Foot Round Slab?
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