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.
Link to this calculator
Contractors, teachers, and forum members are welcome to share this page. Copy the snippet below to credit the source.
<a href="https://diymaterialcalculators.com/concrete-slab/">Concrete Slab Calculator</a> — free online calculator