How Much Concrete for a 28x28 Garage Slab?
For a 28x28 garage slab poured 5 inches thick, plan on about 12.10 cubic yards of concrete. That comes from 784 square feet times 0.417 feet of depth, divided by 27. How much concrete for a 28x28 garage slab at other thicknesses is in the table below.
Concrete calculator →The math for a 28x28 garage slab
- Area: 28 ft × 28 ft = 784 sq ft.
- Thickness in feet: 5 in ÷ 12 = 0.417 ft.
- Volume: 784 × 0.417 = 326.7 cubic feet.
- Cubic yards: 326.7 ÷ 27 = 12.10 yd³.
- With 10% extra: 13.31 yd³.
The concrete calculator runs the same steps for any size and thickness.
Related: How Much Concrete for a 12x20 Garage Slab?
Concrete for a 28x28 garage slab by thickness
| Thickness | Cubic feet | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 261.3 | 9.68 | 10.65 | 436 | 581 |
| 5 in | 326.7 | 12.10 | 13.31 | 545 | 726 |
| 6 in | 392.0 | 14.52 | 15.97 | 654 | 872 |
Bag counts assume about 0.60 cubic feet per 80 lb bag and 0.45 per 60 lb bag, rounded up.
How thick to pour it
Garage floors are commonly 4 to 6 inches thick; 5 inches is a practical middle for cars and light trucks, and 6 inches suits heavier vehicles or a shop with equipment. Check local code, since some areas set a minimum.
Related: How Much Concrete for a 12x24 Garage Slab?
Truck or bags?
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.
Prep before the pour
Under the slab, most residential pours sit on about 4 inches of compacted gravel. The base spreads the load, drains water away and keeps the garage slab from cracking as the soil freezes and thaws. Compact the base in thin lifts, and dampen it just before the pour so it does not pull water out of the mix.
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 28x28 garage slab at 4 inches?
About 9.68 cubic yards, or 10.65 with 10 percent extra.
How many yards for a 28x28 garage slab at 6 inches?
About 14.52 cubic yards.
How many 80 lb bags for a 28x28 garage slab?
About 436 bags at 4 inches thick, before any waste allowance.
How many square feet is a 28x28 garage slab?
784 square feet.
Should I add extra for waste?
Yes. Adding 5 to 10 percent covers uneven base, spillage and form bulges.
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 26x26 Garage Slab?
- How Much Concrete for a 26x28 Garage Slab?
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