How Much Concrete for a 20x24 Garage Slab?
For a 20x24 garage slab poured 5 inches thick, plan on about 7.41 cubic yards of concrete. That comes from 480 square feet times 0.417 feet of depth, divided by 27. How much concrete for a 20x24 garage slab at other thicknesses is in the table below.
Concrete calculator →The math for a 20x24 garage slab
- Area: 20 ft × 24 ft = 480 sq ft.
- Thickness in feet: 5 in ÷ 12 = 0.417 ft.
- Volume: 480 × 0.417 = 200.0 cubic feet.
- Cubic yards: 200.0 ÷ 27 = 7.41 yd³.
- With 10% extra: 8.15 yd³.
The concrete calculator runs the same steps for any size and thickness.
Related: How Much Concrete for a 20x24 Patio?
Concrete for a 20x24 garage slab by thickness
| Thickness | Cubic feet | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 160.0 | 5.93 | 6.52 | 267 | 356 |
| 5 in | 200.0 | 7.41 | 8.15 | 334 | 445 |
| 6 in | 240.0 | 8.89 | 9.78 | 400 | 534 |
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
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.
Getting the ground ready
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, mesh and rebar
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 20x24 garage slab at 4 inches?
About 5.93 cubic yards, or 6.52 with 10 percent extra.
How many yards for a 20x24 garage slab at 6 inches?
About 8.89 cubic yards.
How many 80 lb bags for a 20x24 garage slab?
About 267 bags at 4 inches thick, before any waste allowance.
How many square feet is a 20x24 garage slab?
480 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 20x20 Garage Slab?
- How Much Concrete for a 20x22 Garage Slab?
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