Concrete Slab Calculator
Calculate cubic yards of concrete needed for a slab. Enter length, width, and thickness to determine how much concrete to order.
Enter slab dimensions to calculate concrete needed.
Concrete Slab Formula
Cubic yards = (Length × Width × Thickness in feet) / 27
Example: 20 ft × 10 ft slab, 4 inches thick.
Volume = (20 × 10 × 0.333) / 27 = 66.7 / 27 ≈ 2.47 cubic yards
Volume = (20 × 10 × 0.333) / 27 = 66.7 / 27 ≈ 2.47 cubic yards
Common Slab Thicknesses
| Application | Thickness |
|---|---|
| Sidewalks / patios | 4 inches |
| Driveways (cars) | 4–5 inches |
| Driveways (trucks) | 5–6 inches |
| Garage floors | 4–6 inches |
| Foundation | 8–12 inches |
FAQ
How much extra should I order?
Order 5–10% extra to account for spillage, uneven subgrade, and form irregularities. Running short mid-pour creates a cold joint that weakens the slab.
How many 80-lb bags per yard?
One cubic yard requires approximately 45 bags of 80-lb premixed concrete.
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Last updated: 2026-08-08