A 10 x 10 slab at the standard 4 inch thickness takes about 62 bags of 80 lb concrete mix, or 82 bags of 60 lb mix: roughly 1.36 cubic yards with a 10 percent waste factor included. At 6 inches thick, it's 92 bags of 80 lb mix, about 2 cubic yards.
Here's where those numbers come from, what they look like for other thicknesses and sizes, and why 62 bags might mean you should be calling a ready-mix truck instead.
The math behind the bag count
A 10 x 10 slab is 100 square feet. At 4 inches (a third of a foot) thick, that's 33.3 cubic feet of concrete. Add 10 percent for waste (uneven subgrade, spillage, slightly bowed forms) and you need about 36.7 cubic feet.
An 80 lb bag of concrete mix yields about 0.60 cubic feet when mixed; a 60 lb bag yields 0.45. Divide it out:
- 36.7 ÷ 0.60 = 62 bags of 80 lb mix
- 36.7 ÷ 0.45 = 82 bags of 60 lb mix
Bag counts by thickness (10 x 10 slab)
| Thickness | Use | Cubic yards | 80 lb bags |
|---|---|---|---|
| 4 in | Patio, walkway, shed pad | 1.36 | 62 |
| 5 in | Light vehicle pad | 1.70 | 77 |
| 6 in | Driveway, garage | 2.04 | 92 |
Other common slab sizes at 4 inches
| Slab | 80 lb bags | Cubic yards |
|---|---|---|
| 8 x 8 | 40 | 0.87 |
| 10 x 10 | 62 | 1.36 |
| 12 x 12 | 88 | 1.96 |
| 10 x 20 | 123 | 2.72 |
| 20 x 20 | 245 | 5.43 |
For any other dimensions, thickness, or waste factor, the concrete slab calculator does this math live and also shows 60 lb bag counts.
Should you really mix 62 bags by hand?
Probably not. Sixty-two bags is over 5,000 pounds of material, mixed one wheelbarrow batch at a time, and a slab poured in batches over several hours is weaker than one poured continuously, because the early batches begin setting before the last ones arrive.
The practical rule: under about one cubic yard, bags make sense; over it, price ready-mix. A 10 x 10 x 4 slab sits right at 1.4 yards, which is truck territory for most people. Expect a small-load fee under 3 to 4 yards, and have your forms braced and helpers scheduled before the truck arrives. Our guide to bags vs ready-mix walks through the full decision.
Don't forget what goes under the slab
A slab is only as good as its base: 4 inches of compacted gravel under a patio slab, with wire mesh or fiber reinforcement in the concrete itself. The gravel calculator sizes the base layer, and if you're setting posts instead of pouring a pad, the concrete footing calculator counts bags per hole.