How Much Concrete for a 30x36 Garage Slab?
How much concrete for a 30x36 garage slab depends on thickness. The garage slab covers 30 × 36 = 1,080 square feet, and at 5 inches thick that is about 16.67 cubic yards, or 18.33 yards with a 10 percent allowance. Mixed from bags, it is roughly 750 bags of 80 lb mix.
Concrete calculator →The math for a 30x36 garage slab
- Area: 30 ft × 36 ft = 1,080 sq ft.
- Thickness in feet: 5 in ÷ 12 = 0.417 ft.
- Volume: 1,080 × 0.417 = 450.0 cubic feet.
- Cubic yards: 450.0 ÷ 27 = 16.67 yd³.
- With 10% extra: 18.33 yd³.
The concrete calculator runs the same steps for any size and thickness.
Related: How Much Gravel for a 30x36 Parking Pad?
Concrete for a 30x36 garage slab by thickness
| Thickness | Cubic feet | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 360.0 | 13.33 | 14.67 | 600 | 800 |
| 5 in | 450.0 | 16.67 | 18.33 | 750 | 1,000 |
| 6 in | 540.0 | 20.00 | 22.00 | 900 | 1,200 |
Bag counts assume about 0.60 cubic feet per 80 lb bag and 0.45 per 60 lb bag, rounded up.
Choosing the thickness
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: Recycled Concrete Aggregate for a 30x36 Parking Pad
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.
Base and forms
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 8 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 30x36 garage slab at 4 inches?
About 13.33 cubic yards, or 14.67 with 10 percent extra.
How many yards for a 30x36 garage slab at 6 inches?
About 20.00 cubic yards.
How many 80 lb bags for a 30x36 garage slab?
About 600 bags at 4 inches thick, before any waste allowance.
How many square feet is a 30x36 garage slab?
1,080 square feet.
How much does a cubic yard of concrete weigh?
Roughly 4,000 pounds, or about 2 tons, for normal-weight concrete.
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 30x30 Garage Slab?
- How Much Concrete for a 30x32 Garage Slab?
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