How Much Concrete for a 30x30 Garage Slab?
How much concrete for a 30x30 garage slab depends on thickness. The garage slab covers 30 × 30 = 900 square feet, and at 5 inches thick that is about 13.89 cubic yards, or 15.28 yards with a 10 percent allowance. Mixed from bags, it is roughly 625 bags of 80 lb mix.
Concrete calculator →The math for a 30x30 garage slab
- Area: 30 ft × 30 ft = 900 sq ft.
- Thickness in feet: 5 in ÷ 12 = 0.417 ft.
- Volume: 900 × 0.417 = 375.0 cubic feet.
- Cubic yards: 375.0 ÷ 27 = 13.89 yd³.
- With 10% extra: 15.28 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 30x30 garage slab by thickness
| Thickness | Cubic feet | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 300.0 | 11.11 | 12.22 | 500 | 667 |
| 5 in | 375.0 | 13.89 | 15.28 | 625 | 834 |
| 6 in | 450.0 | 16.67 | 18.33 | 750 | 1,000 |
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
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?
Ordering ready-mix
Ready-mix is priced and batched by the cubic yard (27 cubic feet). Plants commonly add a small-load fee when an order is under a set minimum, so ask about it when you call. Ordering a little extra costs far less than a second truck.
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, mesh and rebar
Reinforcement does not stop cracks, but it holds them tight. Wire mesh or rebar set mid-depth on chairs is common for a garage slab that carries vehicles; fiber-reinforced mix is an option for light-duty slabs. Joints about 8 feet apart control where cracks form.
Questions people ask
How many yards of concrete for a 30x30 garage slab at 4 inches?
About 11.11 cubic yards, or 12.22 with 10 percent extra.
How many yards for a 30x30 garage slab at 6 inches?
About 16.67 cubic yards.
How many 80 lb bags for a 30x30 garage slab?
About 500 bags at 4 inches thick, before any waste allowance.
How many square feet is a 30x30 garage slab?
900 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 28x28 Garage Slab?
- How Much Concrete for a 28x30 Garage Slab?
As an Amazon Associate, AsphaltTons.com earns from qualifying purchases. Product links below are sponsored.