Concrete needed for a 8 × 8 ft slab, by thickness
These figures are for the whole 64 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 | 21.3 | 0.79 | 36 | 48 | 0.87 |
| 5 in | 26.7 | 0.99 | 45 | 60 | 1.09 |
| 6 in | 32.0 | 1.19 | 54 | 72 | 1.30 |
| 8 in | 42.7 | 1.58 | 72 | 95 | 1.74 |
What a 8 × 8 slab is used for
An 8 × 8 ft slab is the classic pad for a hot tub or spa, and also suits a small shed or a cozy patio. A filled hot tub weighs thousands of pounds, so check the manufacturer's slab requirements. Many call for a reinforced slab at least 4 inches thick.
Bags or ready-mix for 8 × 8 ft?
At 0.87 cubic yards you are on the border. 40 bags of 80 lb mix is about 1.6 tons of dry material to mix and place before it sets. Many people still do it with a rented mixer and a few helpers, but get a ready-mix quote as well, since delivery fees and short-load charges can make the two options close.
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 0.95 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 8 × 8 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 8x8 slab?
For a 4 inch slab you need 36 bags of 80 lb concrete (48 bags of 60 lb), or 40 bags of 80 lb with 10% waste. For a 6 inch slab it is 54 bags of 80 lb, or 59 with 10% waste.
How many cubic yards is a 8x8 slab?
A 8 × 8 ft slab is 0.79 yd³ at 4 inches, 0.99 yd³ at 5 inches and 1.19 yd³ at 6 inches, before waste. Add 5 to 10% when you order.
How much does a 8x8 concrete slab weigh?
At 4 inches thick it weighs roughly 3,200 lb (1.6 tons), at about 150 lb per cubic foot. At 6 inches it is about 4,800 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.