Concrete needed for a 6 × 6 ft slab, by thickness
These figures are for the whole 36 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 | 12.0 | 0.44 | 20 | 27 | 0.49 |
| 5 in | 15.0 | 0.56 | 25 | 34 | 0.61 |
| 6 in | 18.0 | 0.67 | 30 | 40 | 0.73 |
| 8 in | 24.0 | 0.89 | 40 | 54 | 0.98 |
What a 6 × 6 slab is used for
A 6 × 6 ft slab is about the size of a small prefab storage shed floor, a firepit surround, or a compact seating area for two. Four inches is enough for a shed or seating pad. Many shed makers recommend a pad a few inches larger than the shed.
Bags or ready-mix for 6 × 6 ft?
At 0.49 cubic yards, bagged concrete is the sensible choice. You will mix about 22 bags of 80 lb, which is manageable in a wheelbarrow or a small mixer, and no truck is needed.
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 0.53 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 6 × 6 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
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Frequently asked questions
How many bags of concrete for a 6x6 slab?
For a 4 inch slab you need 20 bags of 80 lb concrete (27 bags of 60 lb), or 22 bags of 80 lb with 10% waste. For a 6 inch slab it is 30 bags of 80 lb, or 33 with 10% waste.
How many cubic yards is a 6x6 slab?
A 6 × 6 ft slab is 0.44 yd³ at 4 inches, 0.56 yd³ at 5 inches and 0.67 yd³ at 6 inches, before waste. Add 5 to 10% when you order.
How much does a 6x6 concrete slab weigh?
At 4 inches thick it weighs roughly 1,800 lb (0.9 tons), at about 150 lb per cubic foot. At 6 inches it is about 2,700 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.