How Much Concrete for a 24x36 Garage Slab?
How much concrete for a 24x36 garage slab depends on thickness. The garage slab covers 24 × 36 = 864 square feet, and at 5 inches thick that is about 13.33 cubic yards, or 14.67 yards with a 10 percent allowance. Mixed from bags, it is roughly 600 bags of 80 lb mix.
Concrete calculator →The math for a 24x36 garage slab
- Area: 24 ft × 36 ft = 864 sq ft.
- Thickness in feet: 5 in ÷ 12 = 0.417 ft.
- Volume: 864 × 0.417 = 360.0 cubic feet.
- Cubic yards: 360.0 ÷ 27 = 13.33 yd³.
- With 10% extra: 14.67 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 24x36 garage slab by thickness
| Thickness | Cubic feet | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 288.0 | 10.67 | 11.73 | 480 | 640 |
| 5 in | 360.0 | 13.33 | 14.67 | 600 | 800 |
| 6 in | 432.0 | 16.00 | 17.60 | 720 | 960 |
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: How Much Concrete for a 12x24 Garage Slab?
Truck or bags?
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.
Keeping cracks under control
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 24x36 garage slab at 4 inches?
About 10.67 cubic yards, or 11.73 with 10 percent extra.
How many yards for a 24x36 garage slab at 6 inches?
About 16.00 cubic yards.
How many 80 lb bags for a 24x36 garage slab?
About 480 bags at 4 inches thick, before any waste allowance.
How many square feet is a 24x36 garage slab?
864 square feet.
Should I add extra for waste?
Yes. Adding 5 to 10 percent covers uneven base, spillage and form bulges.
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 24x30 Garage Slab?
- How Much Concrete for a 24x32 Garage Slab?
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