How much concrete a slab needs depends on its length, width and thickness. These pages work out common sizes at 4, 5 and 6 inches thick, in cubic yards and in bags.
| Slab | Square feet | 4 in, cu yd | 6 in, cu yd |
|---|---|---|---|
| 10 by 10 ft | 100 | 1.23 | 1.85 |
| 10 by 12 ft | 120 | 1.48 | 2.22 |
| 12 by 12 ft | 144 | 1.78 | 2.67 |
| 12 by 16 ft | 192 | 2.37 | 3.56 |
| 12 by 20 ft | 240 | 2.96 | 4.44 |
| 16 by 16 ft | 256 | 3.16 | 4.74 |
| 20 by 20 ft | 400 | 4.94 | 7.41 |
| 24 by 24 ft | 576 | 7.11 | 10.67 |
The table shows the volume before any extra. For another size, or to add extra for waste, use the concrete calculator.
Reading the sizes
The sizes run from a small pad to a double-car slab. The cubic yards double when the area doubles, and go up by half when you move from 4 to 6 inches thick, because volume is area times thickness.
See also the gravel calculator for the base and the method for how the numbers are worked out.