Concrete Slab Calculator
A standard 4-inch residential slab needs roughly 0.012 cubic yards per square foot—a 10×10 takes about 1.23 yards, a 20×20 takes just under 5. Enter your dimensions to get exact cubic yards, bag count, and cost.
Dimensions
Pro Tips
- →Most residential slabs need 4-6 inches thickness
- →Add 10% extra concrete for waste
- →Include wire mesh or rebar for reinforcement
- →Compact gravel base to 4-6 inches
- →Use control joints to manage cracking
For general step-by-step instructions, read our complete How To Calculate Concrete and How Thick Should Concrete Be.
This calculator estimates concrete for any rectangular slab: patios, garage floors, driveways, walkways, and shed bases. Enter your dimensions and thickness to get cubic yards, cubic feet, bag count, and a rough cost estimate based on current ready-mix pricing.
What the Numbers Mean
Cubic yards is how ready-mix concrete is sold. A 4-inch slab needs approximately 0.012 cubic yards per square foot. A 10×10-foot slab at 4 inches needs about 1.23 cubic yards; a 20×20 needs just under 5. Always order 10% extra for spillage, uneven subgrade, and form overfill.
Bag count applies when mixing on-site. An 80-lb bag yields roughly 0.60 cubic feet (0.022 cubic yards). For anything over 1 cubic yard—roughly a 10×10 at 4 inches—ready-mix delivery is usually faster and cheaper than hand-mixing bags.
Thickness by Use Case
| Use | Thickness | Notes |
|---|---|---|
| Patio / walkway | 4 in | Standard for foot traffic |
| Driveway | 5–6 in | Supports passenger vehicle weight |
| Garage floor | 5–6 in | Use 4,000–5,000 PSI mix |
| RV pad / heavy equipment | 6–8 in | Typically requires engineered design |
Reinforcement and Mix
For a standard 4-inch residential slab, 4,000 PSI concrete with 6×6 wire mesh (W1.4) provides adequate crack resistance. Driveways and garage floors benefit from fiber-reinforced mix or #3 rebar on 18-inch centers. In freeze-thaw climates, specify air-entrained concrete with 5–7% air content to prevent surface scaling.
For full estimation guidance, see how to calculate concrete and how thick should concrete be. For a driveway-specific estimate, use the concrete driveway calculator.