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.
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. Slabs over about 10 cubic yards (one full truck) are typically broken into sections at planned construction joints so the crew can finish each pour within its set window.
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.