Concrete Slab Calculator
Enter your slab's length, width, and thickness to find out how many cubic yards of concrete to order — or how many bags you need.
Results
- Cubic yards
- 1.78 yd³
- Cubic feet
- 48.0 ft³
- Weight
- 3.60 tons
- Bags
- 80 × 80 lb bag
Assumed density: 4050 lb/yd³ (Concrete (wet mix))
How it works
Enter slab length and width in feet. Enter thickness in inches (typical slabs are 4 inches).
The calculator computes volume in cubic feet, then converts to cubic yards (÷ 27).
For ready-mix orders, round up to the nearest 0.25 yards. For bags, use the concrete bag calculator.
Reference chart
Concrete coverage by slab thickness
| Thickness (in) | 1 yd³ covers (sq ft) |
|---|---|
| 3 | 108 |
| 4 | 81 |
| 5 | 65 |
| 6 | 54 |
| 8 | 41 |
Frequently asked questions
How many cubic yards of concrete do I need for a 12×12 ft slab, 4 inches thick?
12 × 12 × (4/12) = 48 cu ft ÷ 27 = 1.78 yd³. Order 2 yards to be safe.
How thick should a concrete patio slab be?
4 inches is standard for patios and walkways. Driveways require at least 5–6 inches to support vehicle weight.
When should I order ready-mix vs. mix my own bags?
Ready-mix is more cost-effective above about 1 cubic yard (about 45 × 80 lb bags). Below that, pre-mixed bags are often cheaper and more convenient.