How Much Concrete for a 24×24 Garage Slab?
Quick Answer
A 24×24 foot garage slab poured 6 inches thick needs 10.67 cubic yards of concrete. Order about 11.7 cubic yards to allow for a 10% waste factor. A slab this large is always a ready-mix delivery job.
- 6-inch garage slab: 10.67 cubic yards (288 cubic feet)
- Order ~11.7 cubic yards with 10% waste
- 4-inch version: 7.11 cubic yards
- Ready-mix cost: $1,600–$2,050 delivered
Formula
Multiply the slab dimensions in feet, then divide by 27 for cubic yards. Garage slabs are typically 6 inches thick to carry vehicle weight, so thickness is 6 ÷ 12 = 0.5 ft.
Step-by-Step Calculation
- 1
Slab area
24 × 24 = 576 square feet
- 2
Volume at 6 inches
576 × 0.5 = 288 cubic feet
- 3
Convert to cubic yards
288 ÷ 27 = 10.67 cubic yards
- 4
Add 10% waste
10.67 × 1.10 = 11.7 cubic yards
24×24 Garage Slab Concrete by Thickness
| Thickness | Cubic Feet | Cubic Yards | With 10% Waste | Ready-Mix Cost* |
|---|---|---|---|---|
| 4 inches | 192 | 7.11 | 7.8 | $1,065–$1,245 |
| 5 inches | 240 | 8.89 | 9.8 | $1,335–$1,555 |
| 6 inches | 288 | 10.67 | 11.7 | $1,600–$1,870 |
*Ready-mix at $150–$175 per cubic yard. A garage slab should be at least 6 inches with rebar or wire mesh reinforcement.
Pro Tips
- A 24×24 garage slab MUST be 6 inches thick with #4 rebar on 18-inch centers both directions — this is not optional. Vehicle loads, jack stands, and heavy tool storage all demand this specification. Some jurisdictions also require thickened edges (8–10 inches) at the perimeter and under load-bearing walls.
- At 10.67 cubic yards (11.7 with waste), coordinate with the ready-mix plant for a continuous pour — you may need two trucks arriving 20 minutes apart. The first truck should arrive full (10 yards), the second with 1.7 yards. Confirm staging with the plant the day before.
- Install a vapor barrier (10-mil poly sheeting, $40–$60 for this size) between the gravel base and concrete. Garages without vapor barriers develop moisture wicking through the slab that causes tools to rust, paint cans to corrode, and stored items to mildew.
- Set the garage slab 4–6 inches above the surrounding grade and slope the slab 1/8 inch per foot toward the garage door. This keeps rainwater and snowmelt from pooling inside.
Key Cost Factors
- Ready-mix concrete for 11.7 yards at $120–$160/yd runs $1,400–$1,870. At this volume you are past the short-load fee and may negotiate a better per-yard rate. Rebar for a 24×24 grid at 18-inch spacing costs $300–$450. Sub-base gravel (6 inches over 576 sq ft = 10.7 yards) costs $370–$535. Total materials: $2,200–$3,100.
- Professional garage slab installation costs $6–$10 per square foot ($3,460–$5,760 for 576 sq ft). The $2,200–$3,100 DIY materials save about $1,300–$2,700 in labor, but this is a large pour requiring a crew of 4–5 people, power screeding, and professional-grade finishing. Not for first-time concrete workers.
Common Mistakes to Avoid
- Pouring it only 4 inches thick. A garage slab that holds vehicles should be 5–6 inches with rebar. Standard patio thickness will crack under car and jack-stand loads.
- Underestimating the volume. A 24×24 slab at 5 inches is about 8.9 cubic yards — nearly a full truck. Ordering short means an expensive second delivery for a small top-up.
- Neglecting the vapor barrier. A garage or shop slab needs a 6-mil poly vapor barrier under it, or moisture will wick up and ruin floor coatings and stored items.
- Forgetting the edge thickening and rebar. Perimeter edges and door thresholds carry the most load and need thickening plus reinforcement.
Related Project Considerations
- Specify a 4,000+ psi mix. Garage floors face vehicle loads, dropped tools, and possibly freeze-thaw at the door, so use a higher-strength mix than a patio.
- Plan the drainage slope. Slope the slab slightly toward the door (about 1/8 inch per foot) so water from tires and washing drains out instead of pooling.
- Add control joints and isolation joints. Saw-cut a grid within 12 hours and isolate the slab from foundation walls so the two can move independently without cracking.
Frequently Asked Questions
How thick should a garage slab be?
A minimum of 4 inches for light-use storage, but 6 inches is strongly recommended for any garage that holds vehicles or heavy equipment. Thicker slabs resist cracking under concentrated wheel loads and last decades longer. Add #4 rebar or welded wire mesh and pour over at least 4 inches of compacted gravel base. Thicken the perimeter edges to 8–10 inches if the slab doubles as the foundation for the garage walls.
How much does a 24×24 garage slab cost?
Materials alone run $1,600–$2,050 at 6 inches thick, including concrete, rebar, and gravel. A fully poured and finished 24×24 garage slab costs $3,500–$8,600 (about $6–$15 per sq ft) with professional labor, reinforcement, base prep, and finishing. The price swings with site conditions — level, well-drained lots are cheapest, while sloped sites needing extra excavation and forming push costs toward the high end.
Do I need rebar in a garage slab?
Yes. Use #4 rebar in a 16 to 24 inch grid placed at mid-depth on rebar chairs, or welded wire mesh (6×6 W2.9×W2.9) as a minimum, to control cracking and carry vehicle loads. Thickened edges around the perimeter — typically 8 to 12 inches deep — add extra strength where wall loads concentrate. Fiber mesh supplements rebar for surface crack control but does not replace structural steel reinforcement.