How Much Concrete for a 28x30 Garage Slab?
How much concrete for a 28x30 garage slab depends on thickness. The garage slab covers 28 × 30 = 840 square feet, and at 5 inches thick that is about 12.96 cubic yards, or 14.26 yards with a 10 percent allowance. Mixed from bags, it is roughly 584 bags of 80 lb mix.
Concrete calculator →The math for a 28x30 garage slab
- Area: 28 ft × 30 ft = 840 sq ft.
- Thickness in feet: 5 in ÷ 12 = 0.417 ft.
- Volume: 840 × 0.417 = 350.0 cubic feet.
- Cubic yards: 350.0 ÷ 27 = 12.96 yd³.
- With 10% extra: 14.26 yd³.
The concrete calculator runs the same steps for any size and thickness.
Related: How Many Tons of Asphalt for a 28x30 Parking Area?
Concrete for a 28x30 garage slab by thickness
| Thickness | Cubic feet | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 280.0 | 10.37 | 11.41 | 467 | 623 |
| 5 in | 350.0 | 12.96 | 14.26 | 584 | 778 |
| 6 in | 420.0 | 15.56 | 17.11 | 700 | 934 |
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 12x20 Garage Slab?
Ordering ready-mix
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
Uneven ground is the main reason pours run short. Every half inch of extra depth across the garage 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
Cut or tool control joints so the slab cracks where you want it to. A common rule is spacing them, in feet, at no more than two to three times the slab thickness in inches, so about 10 feet apart for a 4-inch slab, and about a quarter of the slab depth deep.
Questions people ask
How many yards of concrete for a 28x30 garage slab at 4 inches?
About 10.37 cubic yards, or 11.41 with 10 percent extra.
How many yards for a 28x30 garage slab at 6 inches?
About 15.56 cubic yards.
How many 80 lb bags for a 28x30 garage slab?
About 467 bags at 4 inches thick, before any waste allowance.
How many square feet is a 28x30 garage slab?
840 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.
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 26x28 Garage Slab?
- How Much Concrete for a 28x28 Garage Slab?
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