How Much Concrete for a 15x28 Slab?
For a 15x28 slab poured 4 inches thick, plan on about 5.19 cubic yards of concrete. That comes from 420 square feet times 0.333 feet of depth, divided by 27. How much concrete for a 15x28 slab at other thicknesses is in the table below.
Concrete calculator →The math for a 15x28 slab
- Area: 15 ft × 28 ft = 420 sq ft.
- Thickness in feet: 4 in ÷ 12 = 0.333 ft.
- Volume: 420 × 0.333 = 140.0 cubic feet.
- Cubic yards: 140.0 ÷ 27 = 5.19 yd³.
- With 10% extra: 5.70 yd³.
The concrete calculator runs the same steps for any size and thickness.
Related: How Much Concrete for a 12x20 Slab?
Concrete for a 15x28 slab by thickness
| Thickness | Cubic feet | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 140.0 | 5.19 | 5.70 | 234 | 312 |
| 5 in | 175.0 | 6.48 | 7.13 | 292 | 389 |
| 6 in | 210.0 | 7.78 | 8.56 | 350 | 467 |
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?
Ordering ready-mix
Concrete is ordered by the cubic yard, and a yard is 27 cubic feet. Ready-mix plants usually sell in quarter- or half-yard steps, so round up to the next step rather than down. Running short in the middle of a pour leaves a cold joint, which is a weak seam in the slab.
Prep before the pour
Uneven ground is the main reason pours run short. Every half inch of extra depth across the slab adds concrete you did not plan for. Screed the base flat, check it with a string line and set the forms to finished height before the truck arrives.
Joints and reinforcement
Plan the joints before the pour. Panels close to square crack less than long, narrow ones, and joint spacing around 10 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 15x28 slab at 4 inches?
About 5.19 cubic yards, or 5.70 with 10 percent extra.
How many yards for a 15x28 slab at 6 inches?
About 7.78 cubic yards.
How many 80 lb bags for a 15x28 slab?
About 234 bags at 4 inches thick, before any waste allowance.
How many square feet is a 15x28 slab?
420 square feet.
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.
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
- Cost to Pour a Concrete Slab: Per Square Foot
- How Much Concrete for a 15x25 Slab?
- How Much Concrete for a 15x26 Slab?
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