Concrete calculator
Enter the size of your slab, footing or post hole to get cubic yards and the number of premix bags. The example is a 10 × 10 ft patio slab, 4 inches thick: 1.23 cubic yards, or 56 bags of 80 lb mix before waste.
Concrete needed
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Volume
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Premix bags needed
| Bag size | Yield per bag | Bags (with waste) |
|---|---|---|
| 40 lb (18.1 kg) | 0.30 cu ft | – |
| 60 lb (27.2 kg) | 0.45 cu ft | – |
| 80 lb (36.2 kg) | 0.60 cu ft | – |
Yields are from the QUIKRETE Concrete Mix data sheet. Other brands are similar, but check the yield printed on your bag. For more than about 1 cubic yard, ready-mix delivery is usually easier than mixing bags.
How the calculator works
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A rectangle's volume is length × width × thickness. A round column is π × radius² × height. Divide cubic feet by 27 to get cubic yards, the unit ready-mix suppliers sell by.
Typical slab thickness
| Use | Common thickness |
|---|---|
| Walkways and patios | 4 in |
| Driveways for cars | 4–6 in |
| Slabs for heavier vehicles | 6 in or more |
These are common starting points, not a design. Local building codes and soil conditions decide the real thickness, reinforcement and base.