Concrete Slab Calculator
A 10×10 ft slab 4 in thick takes about 1.36 cubic yards of concrete with a 10% margin: 62 bags of 80 lb mix or 82 bags of 60 lb. Enter your slab size to get bags, ready-mix yards and the gravel base, rounded up to what you can buy.
Concrete
1.36 yd³
80 lb bags
62
60 lb bags
82
- 62 bags
Concrete mix, 80 lb
- 82 bags
Concrete mix, 60 lb
- 123 bags
Concrete mix, 40 lb
- 1.36 yd³
Ready-mix concrete
36.7 ft³
- 1.36 yd³
Base gravel
≈ 1.91 tons
Bagged and bulk options are alternatives — the total uses the cheapest one you price.
How we calculate this
Volume = length (ft) × width (ft) × thickness (in ÷ 12), plus your waste margin (10% by default) for uneven ground and spillage. We divide by 27 for cubic yards, and by each bag's cured yield for bag counts: 0.6 ft³ for an 80 lb bag, 0.45 ft³ for 60 lb and 0.3 ft³ for 40 lb, rounded up. The gravel base uses the same area at your base depth, at about 1.4 tons per cubic yard.
Estimates only. Check local codes and product labels. This calculator is for small flatwork like patios, walkways and shed pads, not for house foundations, driveways or anything structural; check with your building department or a professional. Read our full disclaimer.
Concrete for common slab sizes
| Slab size | Thickness | Cubic yards | 80 lb bags | 60 lb bags |
|---|---|---|---|---|
| 4×4 ft | 4 in | 0.22 | 10 | 14 |
| 8×8 ft | 4 in | 0.87 | 40 | 53 |
| 10×10 ft | 4 in | 1.36 | 62 | 82 |
| 10×12 ft | 4 in | 1.63 | 74 | 98 |
| 12×12 ft | 4 in | 1.96 | 88 | 118 |
| 12×16 ft | 4 in | 2.61 | 118 | 157 |
| 10×10 ft | 6 in | 2.04 | 92 | 123 |
| 12×12 ft | 6 in | 2.94 | 132 | 176 |
FAQ
How many bags of concrete do I need for a 10×10 slab?
A 10×10 ft slab 4 in thick is 33.3 cu ft of concrete. With a 10% margin that's about 36.7 cu ft (1.36 cubic yards): 62 bags of 80 lb mix, 82 bags of 60 lb or 123 bags of 40 lb.
How many bags of concrete are in a cubic yard?
A cubic yard is 27 cu ft, so it takes 45 bags of 80 lb mix (0.6 cu ft each), 60 bags of 60 lb (0.45 cu ft) or 90 bags of 40 lb (0.3 cu ft), before any waste margin. Check the yield printed on the bag you buy.
How thick should a concrete patio or shed slab be?
4 in is the usual thickness for patios, walkways and small shed pads. Slabs that carry heavier loads, such as a hot tub or a vehicle, need more thickness and often reinforcement; local code and the equipment maker's instructions decide that.
Do I need gravel under a concrete slab?
A compacted gravel base, commonly about 4 in, gives the slab even support and helps drainage, especially on clay or poorly drained soil. The calculator adds a 4 in base by default; set it to 0 if your plans call for none.
Should I use bags or order ready-mix?
Bags suit small pours you can mix in a wheelbarrow or rented mixer. One cubic yard is already 45 bags of 80 lb, about 3,600 lb of mix, so for larger slabs compare a ready-mix delivery quote. Many suppliers charge extra for small loads. Enter both prices in the shopping list to compare.
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