Pouring a slab
The calculator above is set to a 12 × 12 ft slab, 4 in thick: a typical patio or shed base. Type your own length, width and thickness. For an L-shaped patio, add a second slab card for the other leg rather than measuring around the corner, and the volumes are added.
Measure the thickness from the top of the compacted base to where the finished surface will be, at several points. Ground is rarely flat, and the concrete fills every dip: a base that sits 1 in low under a 4 in slab adds a quarter to the concrete over that area. If your measurements vary, use the average, or keep the 10% extra.
How thick, and where the joints go
Quikrete’s FAQ gives the usual thickness for a patio, sidewalk or driveway as the height of a 2 × 4, about 3½ in, and Quikrete’s own mix is designed for pours 2 in or more thick. A slab that carries a car, a hot tub or a shed full of tools is often poured thicker; the table below shows how fast that adds up.
Control joints let the slab crack where you want it to. Quikrete’s guide spaces them at the slab’s thickness in inches × 2.5 feet apart, and cuts them a quarter of the slab’s depth.
Bags or a truck
The table gives 80 lb bags because they’re the most common size in the US; pick a lighter bag in the calculator to see the count in 40, 50 or 60 lb. Past a cubic yard, that’s more than 45 bags to carry and mix: worth comparing with a ready-mix quote.
Concrete for common slab sizes
Each cell: the slab's volume, then the 80 lb bags of Quikrete Concrete Mix (0.60 cu ft each) to buy with 10% extra.
| Slab | 3.5 in thick | 4 in thick | 5 in thick | 6 in thick |
|---|---|---|---|---|
| 8 × 8 ft | 0.69 yd³ · 35 | 0.79 yd³ · 40 | 0.99 yd³ · 49 | 1.19 yd³ · 59 |
| 10 × 10 ft | 1.08 yd³ · 54 | 1.23 yd³ · 62 | 1.54 yd³ · 77 | 1.85 yd³ · 92 |
| 10 × 12 ft | 1.3 yd³ · 65 | 1.48 yd³ · 74 | 1.85 yd³ · 92 | 2.22 yd³ · 110 |
| 12 × 12 ft | 1.56 yd³ · 77 | 1.78 yd³ · 88 | 2.22 yd³ · 110 | 2.67 yd³ · 132 |
| 10 × 20 ft | 2.16 yd³ · 107 | 2.47 yd³ · 123 | 3.09 yd³ · 153 | 3.7 yd³ · 184 |
| 16 × 16 ft | 2.77 yd³ · 137 | 3.16 yd³ · 157 | 3.95 yd³ · 196 | 4.74 yd³ · 235 |
| 20 × 20 ft | 4.32 yd³ · 214 | 4.94 yd³ · 245 | 6.17 yd³ · 306 | 7.41 yd³ · 367 |
| 24 × 24 ft | 6.22 yd³ · 308 | 7.11 yd³ · 352 | 8.89 yd³ · 440 | 10.67 yd³ · 528 |
| Slab | 7.5 cm thick | 10 cm thick | 12.5 cm thick | 15 cm thick |
|---|---|---|---|---|
| 2 × 2 m | 0.3 m³ · 33 | 0.4 m³ · 44 | 0.5 m³ · 55 | 0.6 m³ · 66 |
| 3 × 3 m | 0.675 m³ · 75 | 0.9 m³ · 99 | 1.125 m³ · 124 | 1.35 m³ · 149 |
| 3 × 4 m | 0.9 m³ · 99 | 1.2 m³ · 132 | 1.5 m³ · 165 | 1.8 m³ · 198 |
| 4 × 4 m | 1.2 m³ · 132 | 1.6 m³ · 176 | 2 m³ · 220 | 2.4 m³ · 264 |
| 3 × 6 m | 1.35 m³ · 149 | 1.8 m³ · 198 | 2.25 m³ · 248 | 2.7 m³ · 297 |
| 5 × 5 m | 1.875 m³ · 207 | 2.5 m³ · 275 | 3.125 m³ · 344 | 3.75 m³ · 413 |
| 6 × 6 m | 2.7 m³ · 297 | 3.6 m³ · 396 | 4.5 m³ · 495 | 5.4 m³ · 594 |