Concrete needed for a 12 × 12 ft slab, by thickness
These figures are for the whole 144 ft² slab. The last column adds 10% for waste, which is what we suggest you order.
| Thickness | Cubic feet | Cubic yards | 80 lb bags | 60 lb bags | Yards with 10% waste |
|---|---|---|---|---|---|
| 4 in | 48.0 | 1.78 | 80 | 107 | 1.96 |
| 5 in | 60.0 | 2.22 | 100 | 134 | 2.44 |
| 6 in | 72.0 | 2.67 | 120 | 160 | 2.93 |
| 8 in | 96.0 | 3.56 | 160 | 214 | 3.91 |
What a 12 × 12 slab is used for
A 12 × 12 ft slab is a generous patio, a base for a 12 × 12 gazebo or pergola, or a floor for a larger shed. Four inches for patios and pergolas. Add control joints so the slab cracks where you want it to.
Bags or ready-mix for 12 × 12 ft?
At 1.96 cubic yards, ready-mix is the sensible choice. Doing it with bags would mean 88 bags (about 3.5 tons of dry mix), which is too much to mix by hand before the first batch starts to set. Ask your supplier about their minimum order and how long you have to unload.
Don't forget what goes under and inside it
A slab needs a compacted base, usually 4 inches of gravel, which for this size is about 2.13 cubic yards after allowing for compaction (see the gravel calculator). Reinforcement such as rebar or wire mesh holds cracks tight: the rebar calculator counts bars for a 12 × 12 ft grid.
Want to change anything else? The calculator above is the full Concrete Calculator: edit any number and the results update instantly.
Tools & materials for this project
As an Amazon Associate we earn from qualifying purchases. These links do not change what you pay.
Frequently asked questions
How many bags of concrete for a 12x12 slab?
For a 4 inch slab you need 80 bags of 80 lb concrete (107 bags of 60 lb), or 88 bags of 80 lb with 10% waste. For a 6 inch slab it is 120 bags of 80 lb, or 132 with 10% waste.
How many cubic yards is a 12x12 slab?
A 12 × 12 ft slab is 1.78 yd³ at 4 inches, 2.22 yd³ at 5 inches and 2.67 yd³ at 6 inches, before waste. Add 5 to 10% when you order.
How much does a 12x12 concrete slab weigh?
At 4 inches thick it weighs roughly 7,200 lb (3.6 tons), at about 150 lb per cubic foot. At 6 inches it is about 10,800 lb.
Related sizes and guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.