How Much Concrete for a 12x28 Slab?
How much concrete for a 12x28 slab depends on thickness. The slab covers 12 × 28 = 336 square feet, and at 4 inches thick that is about 4.15 cubic yards, or 4.56 yards with a 10 percent allowance. Mixed from bags, it is roughly 187 bags of 80 lb mix.
Concrete calculator →The math for a 12x28 slab
- Area: 12 ft × 28 ft = 336 sq ft.
- Thickness in feet: 4 in ÷ 12 = 0.333 ft.
- Volume: 336 × 0.333 = 112.0 cubic feet.
- Cubic yards: 112.0 ÷ 27 = 4.15 yd³.
- With 10% extra: 4.56 yd³.
The concrete calculator runs the same steps for any size and thickness.
Related: How Much Concrete for a 12x20 Slab?
Concrete for a 12x28 slab by thickness
| Thickness | Cubic feet | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 112.0 | 4.15 | 4.56 | 187 | 249 |
| 5 in | 140.0 | 5.19 | 5.70 | 234 | 312 |
| 6 in | 168.0 | 6.22 | 6.84 | 280 | 374 |
Bag counts assume about 0.60 cubic feet per 80 lb bag and 0.45 per 60 lb bag, rounded up.
Thickness for this job
Four inches is the usual thickness for patios, walks and shed floors. Slabs that carry cars or a heavy hot tub are often poured at 5 to 6 inches, and edges are sometimes thickened where loads concentrate.
Related: How Much Concrete for a 12x24 Slab?
Placing the order
A cubic yard of concrete is 27 cubic feet and weighs roughly 4,000 pounds. Most ready-mix trucks carry up to about 9 to 10 yards, though local trucks and rules vary. If your total is under a yard or two, bagged mix or a short-load supplier may be cheaper.
Base and forms
Prep matters as much as the yardage. Strip sod and soft soil, compact the subgrade, then add a compacted stone base, commonly about 4 inches. A level, firm base also keeps your thickness even, which keeps the yardage close to the math.
Joints and reinforcement
Plan the joints before the pour. Panels close to square crack less than long, narrow ones, and joint spacing around 8 feet is typical for a 4-inch slab. Cut joints with a groover while the concrete is soft or with a saw within the first day.
Questions people ask
How many yards of concrete for a 12x28 slab at 4 inches?
About 4.15 cubic yards, or 4.56 with 10 percent extra.
How many yards for a 12x28 slab at 6 inches?
About 6.22 cubic yards.
How many 80 lb bags for a 12x28 slab?
About 187 bags at 4 inches thick, before any waste allowance.
How many square feet is a 12x28 slab?
336 square feet.
Should I add extra for waste?
Yes. Adding 5 to 10 percent covers uneven base, spillage and form bulges.
When is bagged concrete practical?
Usually for jobs under about a cubic yard. Beyond that, mixing dozens of bags by hand gets slow and batches may not blend well.
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
- Cost to Pour a Concrete Slab: Per Square Foot
- How Much Concrete for a 12x25 Slab?
- How Much Concrete for a 12x26 Slab?
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