Cubic yards and bags for a slab, patio or driveway
Bag yields: 0.60, 0.45 and 0.30 ft³ for 80, 60 and 40 lb premix. Waste included.
Volume (yd³) = length (ft) × width (ft) × thickness (in) ÷ 12 ÷ 27. In metric, length (m) × width (m) × thickness (mm) ÷ 1000 gives m³.
| Thickness | Cubic yards | 80 lb bags |
|---|---|---|
| 3.5 in | 1.08 | 49 |
| 4 in | 1.23 | 56 |
| 5 in | 1.54 | 70 |
| 6 in | 1.85 | 84 |
| 8 in | 2.47 | 112 |
No waste included. For footings, columns, walls or stairs, use the full concrete calculator.
At 4 in thick, 10 × 10 × 0.333 = 33.3 ft³, which is 1.23 yd³ or 56 bags of 80 lb premix. Add 5 to 10 percent for waste.
Patios, walks and shed floors are usually 4 in. Driveways and garage floors carrying cars are often 5 to 6 in. Heavier loads need an engineered design.
Past about 1 yd³ (45 bags of 80 lb), ready-mix is usually cheaper and gives a more uniform slab. Many suppliers have a minimum order or a short-load fee below 3 to 4 yd³.
Slabs on grade usually get #3 or #4 bars at 12 to 18 in each way, or welded wire mesh, mainly to hold shrinkage cracks tight. The rebar calculator gives the bar count and weight.