How much concrete do I need for a 8×8 slab?
A 8 × 8 ft slab poured 4 inches thick needs 0.87 cubic yards of concrete, which is 40 bags of 80 lb mix or 53 bags of 60 lb. That includes 10 percent extra for an uneven base; the exact volume is 0.79 cubic yards (21.3 cubic feet). At 6 inches, for a driveway or garage, it is 1.30 cubic yards or 59 bags of 80 lb.
Concrete for a 8×8 slab by thickness
| Thickness | Exact volume | Order (10% extra) | 80 lb bags | 60 lb bags | 50 lb bags | 40 lb bags |
|---|---|---|---|---|---|---|
| 4 in | 0.79 cu yd (21.3 cu ft) | 0.87 cu yd | 40 | 53 | 63 | 79 |
| 5 in | 0.99 cu yd (26.7 cu ft) | 1.09 cu yd | 49 | 66 | 79 | 98 |
| 6 in | 1.19 cu yd (32.0 cu ft) | 1.30 cu yd | 59 | 79 | 94 | 118 |
Bag counts are rounded up and include the same 10 percent allowance. One 80 lb bag yields 0.60 cubic feet; 60 lb yields 0.45; 50 lb yields 0.375; 40 lb yields 0.30.
Change the numbers
The calculator below is preset for this size. Adjust anything and the results update instantly.
Bags or a ready-mix truck for a 8×8 slab?
At 40 bags of 80 lb, mixing by hand is realistic: that is about 1.6 tons of material and roughly 2.0 hours of mixing at three minutes a bag, so plan on two people and a rented mixer. Bags will cost about $260 at $6.50 each. A ready-mix truck would charge for a short load on 0.87 yards, typically $109 to $152 for the concrete plus a $75 to $150 short-load fee, so bags usually win on price for a slab this size unless you value the time saved.
Everything else a 8×8 slab needs
- Gravel base: 4 in of compacted crushed stone over 64 sq ft is 0.87 cubic yards, about 1.3 tons. See the gravel calculator.
- Reinforcement: wire mesh in 5 × 10 ft sheets (2 sheets) or #4 rebar on a 16 in grid, about 90 linear feet. The rebar calculator prices it out.
- Forms: 32 linear feet of 2 × 4 (5 eight-footers) with a stake every 2 ft, about 16 stakes.
- Vapor barrier: 74 sq ft of 6 mil plastic if the slab is for a shed, garage, or anything enclosed.
- Control joints: none needed; a 4 in slab can go 10 ft between joints and this one is within that.
- Expansion joint: 1/2 in fiber strip wherever the slab meets a house, driveway, or other concrete.
How the numbers are figured
8 × 8 ft is 64 square feet. Multiply by the thickness in feet (4 in is 0.333 ft) for cubic feet, divide by 27 for cubic yards, and add 10 percent because a gravel base is never perfectly flat. Bag counts divide the cubic feet by each bag's yield. The concrete calculator above does the same math for any size, shape, or waste factor.
Common questions
How many 80 lb bags of concrete for a 8x8 slab?
40 bags at 4 inches thick, 49 bags at 5 inches, or 59 bags at 6 inches, each including 10 percent extra. In 60 lb bags the 4 inch slab takes 53.
How much does concrete for a 8x8 slab cost?
About $260 in 80 lb bags at $6.50 each, or $109 to $152 for 0.87 yards of ready-mix before any short-load fee. Having a contractor form, pour, and finish it typically runs $384 to $640, or $6 to $10 per square foot.
How thick should a 8x8 concrete slab be?
4 inches for a patio, walkway, shed floor, or hot tub pad on well-compacted gravel. Go to 5 or 6 inches if cars will drive on it, and 6 inches with rebar for a garage, workshop with heavy tools, or RV pad. For a 8×8 slab the jump from 4 to 6 inches adds 0.43 cubic yards.